The Locked Room

The Baker Street Mysteries #3

by Holly Hepburn

The BRAND NEW instalment in Holly Hepburn's Baker Street Mystery series - for fans of Sherlock Holmes! Join Harriet White in 1930's London for another glorious Sherlock Holmes-inspired mystery, for fans of Nita Prose and Janice Hallett.

After a very close call on the Cambridgeshire Fens, Harriet White is about ready to hang up her deerstalker and settle back into her normal life, working in a bank on Baker Street. Until she discovers a letter in The Times newspaper challenging Sherlock Holmes to prove his status as the world’s greatest detective, by solving an impossible mystery. The letter, signed Professor James Moriarty, advises Holmes that the crime will be committed within the following seven days. There will be no further clues – Holmes himself must deduce which crime is the correct one to investigate.

Dismissing the letter as a prank, Harry goes about her business until news breaks of the theft of valuable jewel collection from a safe in an apparently locked room in a Mayfair townhouse.

Intrigued in spite of her misgivings, Harry dons a disguise and investigates. But as she begins to unpick the puzzle, a body is found. And now, a stranger, and far more deadly mystery begins to unfold around her...

Genres: Mystery, Historical Fiction, Crime

217 pages, Kindle Edition

Expected publication January 20, 2026

About the author

I’ve wanted to write books for adults for as long as I can remember but I was too scared to try. One day I decided to be brave and dipped a toe into the bubble bath of romantic comedy with my first novella, Cupidity, and I’ve never looked back. I often try to be funny to be funny, except for when faced with traffic wardens and border control staff. My favourite thing is making people smile.

I’ve tried many jobs over the years, from barmaid to market researcher and I even had a brief flirtation with modelling. These days I am mostly found writing.

I live near London with my grey tabby cat, Portia. We both have an unhealthy obsession with Marmite.

Reviews

[Kimberly · Rating 5 out of 5]

Book review: Holly Hepburn, The Locked Room.
Boldwood Books, with sincere thanks to the publisher and NetGalley for my gifted ARC.

There is something endlessly comforting about slipping back into Holly Hepburn’s version of 1930s London, and The Locked Room made me feel instantly at home. This is the third book in the Baker Street Mystery series, and while longtime readers will enjoy seeing familiar faces again, it also works beautifully as a standalone. From the very first chapter, I was reminded why this series is such a clever and cozy twist on classic detective fiction. Letters still arrive for Sherlock Holmes at Baker Street, and Harriet “Harry” White is the woman tasked with answering them. Except, of course, Harry has a habit of doing far more than replying politely.

This time, the mystery begins with a public provocation. A letter signed by “Professor Moriarty” appears in The Times, daring Sherlock Holmes to solve a crime that has not yet been committed. Harry dismisses it as a prank until a priceless diamond disappears from a safe in a Mayfair townhouse, a theft that appears impossible. The locked-room setup is irresistible, and Hepburn leans into it with confidence, giving readers a puzzle that feels fair, intriguing, and satisfyingly knotty without becoming overly complex.

What I love most about this series is the balance. Yes, there is danger, deception, and even murder, but the story never loses its warmth. Harry investigates in disguise, asks awkward questions, and follows her instincts even when common sense tells her to stop. Alongside the central mystery, there are family concerns, social expectations, and a gentle but persistent romantic undercurrent that adds emotional texture without overwhelming the plot. The personal stakes matter just as much as the crime, and that’s what makes this feel like more than just a puzzle to solve.

Hepburn’s writing is witty and smooth, with a light touch that keeps the pages turning. The historical setting feels natural rather than showy. I could picture the grand houses, the quieter streets, and the contrast between wealth and hardship in London at the time. Small details bring the era to life, and I appreciated how seamlessly they were woven into the story instead of being dropped in for effect.

Harry herself continues to be a standout protagonist. She’s clever but not infallible, brave without being reckless for the sake of it, and refreshingly human. I enjoyed watching her navigate expectations placed on her while quietly pushing against them. The supporting cast adds depth and charm, and I found myself genuinely invested in their lives as well as the mystery at hand.

“There’s something deeply satisfying about a mystery that invites you in, pours you a cup of tea, and then quietly pulls the rug out from under your feet.”

By the time I reached the final reveal, I was fully hooked. The solution made sense, the clues were there, and I immediately wanted to flip back and see how neatly everything had been laid out. The Locked Room is exactly what I want from a historical cozy mystery: smart, comforting, engaging, and just twisty enough to keep me guessing. Fans of Sherlock Holmes-inspired stories, locked-room mysteries, and character-driven historical fiction should absolutely add this to their reading list.

⭐️⭐️⭐️⭐️⭐️ 5 stars

#TheLockedRoom #HollyHepburn #BookReview #HistoricalMystery #CozyMystery #LockedRoomMystery #BakerStreetMystery #SherlockInspired #NetGalley #BoldwoodBooks #ARCReview

[June Price · Rating 5 out of 5]

First, I want to tell readers that such a job as held here by Harriet "Harry" White really did exist. Make sure you read the Author's Note before you dive into the book for more on that and some other relevant notes. Once you dive into the book, whether as a returning reader or a newbie, you're in for quite a ride. Harry, the grand-daughter of a baron, hardly fits the expected mold for women in 1930's London. She's smart, curious, independent, living on her own, and just can't resist answering the occasional letter herself as Holmes' assistant that she's been given to respond to for the fictional Sherlock Holmes and getting involved in investigating the "case". She's smart enough to know she doesn't have the latitude of Doyle's Holmes and can't do it all on her own. While not exactly fool hardy, she does seem to get herself into some tricky, dangerous situations, especially for a lady of her social status in England. Fortunately, she has two sleuthing buddies, with Beth playing a prominent and seemingly permanent role this go-round.

I don't want to dive too far into the plot as it'll be far more fun to discover it as you read but will say it starts with not a letter to Holmes but an advertisement/announcement in the newspaper from none other than Professor James Moriarty, Holmes nemesis. While assuming it's just a fun taunt, the game becomes deathly serious with not just the theft of a diamond but death. Watching Harry and Oliver, plus Beth, work their way through the clues and red herrings is fun and you'll get a tour of some old style gambling dens and underground London in the process. Harry is also trying to sort out her youngest brother Rufus' latest potential scandal, something that leads Harry into a side of London respectable young women didn't frequent. Wait to you see how she manages this. Oliver is right there beside her for much of this and has a few revelations of his own that startle Harry. Sometimes it's tough to disguise your feelings.

Okay, not saying much more other than that the visits themselves are wonderfully described and, oh, you will even get to experience a circus of the time. Cotton candy, anyone? I liked the characters and it was nice to get to know her brother Seb a bit better as well as Percy, Harry's mother's choice for a son-in-law. Oh, and Harry meets Scotland Yard's Inspector Wells, who you'll surely enjoy getting to know. The author does a great job setting the scene and I felt like I was right there with the characters on the streets and, well, elsewhere. As noted, the book works well as a standalone, so don't hesitate to jump in there. You'll be quickly caught up on the cast of characters and some of the social divisions of the time. The mystery is clever and, oh, so devious. Thanks #BoldwoodBooks and #NetGalley for this early peek back into time to catch up on Harry's life. The ending already has me ready for the next episode.

[Pattie Tierney · Rating 5 out of 5]

I’d never picked up a Holly Hepburn book before The Locked Room. Three days later I was bleary-eyed, ignoring my family, and completely obsessed. This book swallowed me whole—I kept sneaking pages at red lights and muttering “just one more chapter” until the wee hours. Even though it’s the third in the series, I never felt lost; old characters pop in like welcome friends, but the story stands beautifully on its own. (That said, I’ve already ordered books one and two because I need more Harry White in my life immediately.)

Imagine a love letter to Sherlock Holmes that somehow feels fresh: real letters still arrive at 221B Baker Street, and clever, fiercely independent Harriet “Harry” White secretly investigates them in Holmes’s name. This time a newspaper dare drags her to a snowbound manor for the most delicious locked-room puzzle I’ve read in years, complete with false identities, impossible footprints, and a subplot about her mischievous little brother that had me grinning even while my pulse raced. Hepburn’s prose is witty, warm, and so evocative I could smell the woodsmoke and taste the brandy. The twists genuinely surprised me, the romance simmers without ever overwhelming the mystery, and the final reveal left me gasping then immediately rereading chapters to see how brilliantly she’d fooled me. If you love Golden Age crime with modern heart—or if you just want to fall hopelessly in love with a stubborn, brilliant heroine—this is your next can’t-put-it-down read. It’s elementary: five stars and zero regrets.

Appreciative thanks to NetGalley, the author, and the publisher for providing me with an advanced digital copy in exchange for an honest review.

[Emily Pankhurst · Rating 5 out of 5]

Netgalley Review

The writing was light and engaging. I was entertained from the beginning right through to the end. 


The chapters were long and occasionally split. This meant that we got a good chunk of the story before moving on. There was quite a lot of information that we were presented with, including a couple of different things that the main character was looking into, but I managed to keep up. It all came together well at the end. 


There was a good flow between the chapters so I was happy to sit and read the story for long periods of time.


There was a good pace to the book despite the long chapters and the amount of information that we were given. There were little time and event jumps that kept the story moving forward well. I was certainly kept on my toes! 


The characters were great. I loved following the main character around London and felt immediately transported to the 1930s with the limited options that she had as an upper class woman. It was interesting to see how she used her male relative and friends' stations in order to get the information that she wanted. It was also interesting to see how she also used the lower class characters to get her information from other places that as an upper class citizen she was unable to frequent herself. All of the information was gathered well and tied up neatly at the end. I would quite happily read more about all of the characters. 


Lastly the settings. I enjoyed being in 1930s London. There were some lovely little details that really added to the story. 


Overall an excellent mystery that I highly recommend. Perfect for any Sherlock Holmes fan who enjoys a twist on the original series.

[Leanne · Rating 4 out of 5]

The Locked Room is a sparkling new instalment in Holly Hepburn’s Baker Street Mystery series, and it’s every bit as atmospheric and clever as fans could hope for. Set in 1930s London, it captures the glamour and grit of the era while weaving a mystery that feels both classic and fresh.

Harriet White is quickly becoming a heroine to root for—resourceful, curious, and just a little daring. Her discovery of a letter in The Times, signed by none other than Professor Moriarty, sets the stage for a deliciously Holmes-inspired puzzle. When a diamond disappears from a locked room and a body soon follows, Harriet finds herself drawn deeper into a case that brims with intrigue, danger, and wit.

Hepburn’s writing balances charm with suspense beautifully. The locked-room setup is handled with flair, and the disguises, clues, and twists all nod to Sherlock Holmes while giving Harriet her own distinctive voice. The London backdrop adds richness, from the bustle of Baker Street to the elegance of Mayfair, making the mystery feel immersive and alive.

The Locked Room is a delightful blend of cozy mystery and classic whodunnit, perfect for fans of Helena Dixon, Nita Prose, and Janice Hallett. It’s witty, atmospheric, and full of heart—a story that proves Harriet White is more than capable of carrying the mantle of Baker Street’s mysteries.

My thanks to Holly Hepburn, the publisher and netgalley for the ARC

[Jeff · Rating 5 out of 5]

Several years ago, I had read that a long time ago, a bank had bought the property with the famous Baker Street address of Sherlock Holmes. But that is not the news. The bank employed someone to answer the mail that came in addressed to the famous detective. According to the author, Holly Hepburn, that was a practice that continued until the early 2000s.

Why does this matter? Because Ms. Hepburn has come up with an incredible premise for a series. What if the person answering the mail addressed to the fictitious Sherlock Holmes actually started investigating (and solving) the cases that were mailed to the bank. “The Locked Room” is the 3rd book in the series.

Harriet “Harry” White and her ragtag group do just that. They solve cases in the name of Sherlock Holmes. And the winner, those that read the series.

Now, don’t assume these are just cute, throw-away cozies. The mystery is worthy of the great detective. The writing is superb. The characters enjoyable.

I thought it was a fun premise. I found myself fully engrossed in the novel. If you are a fan of Sherlock Holmes, or dare I say great mysteries, this book is for you. It’s elementary.

Thank you to NetGalley and the Publisher for providing an ARC for an unbiased review.

[Stephanie · Rating 4 out of 5]

The Locked Room is the third installment in Holly Hepburn’s series, and while it didn’t quite reach the highs of the earlier books for me, it was still a pleasant and engaging read. Hepburn’s writing remains warm, accessible, and comforting, making this a book that’s easy to settle into—even during a reading slump.

The story continues to build on familiar characters and settings, offering a sense of continuity that longtime readers of the series will appreciate. While the plot felt quieter and less stimulating than the first two books, it still held my attention better than several other recent reads, which speaks to Hepburn’s ability to create an inviting narrative flow.

This installment leans more toward gentle progression than dramatic momentum, focusing on atmosphere, relationships, and small emotional shifts rather than high-stakes tension. For readers who enjoy character-driven stories and a softer pace, this will still feel like a comforting return to a familiar world.

Overall, The Locked Room may not be the strongest entry in the series, but it’s a solid and enjoyable continuation—one that will likely appeal most to fans already invested in these characters and their journeys.

Thanks to Netgalley and Boldwood books for this ARC, this is my honest review.

[Laurel Kristick · Rating 4 out of 5]

This is a delightful historical mystery with a great protagonist - Harry White, an independent young woman in 1930s London whose job is answering the many letters to Sherlock Holmes received at the bank located where 221B Baker Street would be. This is the third book in the series, but read well as stand alone. The references to the earlier books were good for setting the background without being tedious or confusing.

In the previous books, it appears Harry would occasionally deviate from the standard response (that Sherlock Holmes was retired) and would answer in the role of Sherlock Holmes' assistant offering to take the case. In this book, Harry is pressured by her family to investigate the mysterious woman her brother is planning on eloping with, intrigued by a jewel theft from a locked room, and drawn to a challenge in the newspaper by a person calling themself Moriarty.

I received this from NetGalley and am grateful to the author and publisher for the opportunity to read this in exchange for an honest review.

[John · Rating 5 out of 5]

This is the third book in "The Baker Street Mysteries" in which Harriet ("Harry") White is the person responsible for answering all the letters addressed to the fictional Sherlock Holmes at 221b. In this book Harry isn't following up on one of the letters begging Holmes' help, but rather a challenge in the newspaper "agony column" addressed to Sherlock Holmes from his arch-rival Moriarty. Since neither of these characters really exists, someone must be sending this message to Harry. And she dives right in with the help of her lawyer friend Oliver, her undercover person Beth, and a bit of Scotland Yard. Disguises and Speakeasys are involved!

I loved this book even more than the previous two, even though it didn't directly involve her job at the bank answering letters. The main characters are likable and believable. The plot is finely crafted and held my interest from beginning to end.

I highly recommend this new series as the author has shown much skill in weaving interesting mysteries.

I obtained an advance copy of this book via NetGalley.

[Valleri · Rating 4 out of 5]

Here we go again, Harry! Harriet White is still working in the post room of a building society at 221B Baker Street and still secretly responds to letters addressed to the fictional Sherlock Holmes. She may have taken it a wee bit farther in The Locked Room, however...

What is Harry to do when a letter appears in The Times from someone claiming to be Professor James Moriarty, who challenges Holmes to solve an "impossible crime" that will occur within a week? That would be everything she CAN do, including donning a disguise so she can pass herself as a man!

I think Harry is a wonderful character, and I also love Harry's new rough-around-the-edges partner, Beth. And then there is Harry's will-they-or-won't-they love interest. The Locked Room is a great addition to The Baker Street Mysteries series!

BIG thanks to #BoldwoodBooks, for providing this book for consideration and review via #NetGalley. All opinions are my own. The Locked Room has an expected publication date of January 20, 2026.

#HollyHepburn #Mystery #HistoricalFiction #Series

[Kate Hardy · Rating 5 out of 5]

Third book in the series but can work as a standalone as Holly catches you up with the characters (but I do recommend the other books, too).

Harriet White answers letters sent to Sherlock Holmes; she's promised not to get involved in any more mysteries, but then Moriarty puts an ad in the Times challenging Holmes to solve an upcoming crime. When a valuable jewel is stolen in Mayfair, Harriet gets involved - and then discovers a dead body...

Great characterisation, a good plot with enough twists and turns and a side drama involving Harry's life, plus a nice romance in progress (which might end up as a love triangle - I know which side I'm on). There's a real flavour of life in 1930s London - both the rich set and the poorer streets. (The rat catcher is excellent.)

Good read. Thank you to Netgalley, the author and the publisher for the ARC.

[Jennifer · Rating 4 out of 5]

The 3rd book in this series didn't disappoint. I enjoy the side characters in the story and Harry's relationships with them. Her brother Seb is a good co-conspirator and it was fun to have him more involved in her investigating. Beth is the perfect side-kick who knows more about the gritty real world of London and can help Harry with tasks that she is less equipt for. Oliver jumps into whatever role she needs and we get some honest conversation about why in this book. I have to admit to some chuckling to Oliver & Harry in their disguises and imagining what it must have looked like. I look forward to Book 4 to find out what happens next!

Thank you to NetGalley and the publisher for selecting me to read an advanced copy.

[Suzan · Rating 5 out of 5]

Holly Hepburn has amazed me yet again. This is book e in the series, and the first two books were five stars for me, and this one is as well. The case for Harry to look into is not a letter this time, sent to 221 Baker Street. I like that it is much more personal. I also love the added Moriaty element added to this book. I also love the way that Holly Hepburn can write a book that continues the story from the other books in the series, yet you can read this book as a standalone without losing anything.
I can't wait for the next in this series to see what Harry will get herself into.
Thank you to Netgalley, Boldwood Books, and the author Holly Hepburn for an advance copy. The review is mine and mine alone.

[Theresa Sivelle · Rating 4 out of 5]

Harry (Harriett) White works at the bank in London located at 221B Banker Street. The bank gets a lot of mail addressed to Sherlock Holmes and Harry is responsible to answer those letters. She has a standard letter, but every now and then a letter comes in that she decides to help with. This time the letter is in the newspaper and it's from Moriarty.

Harry is a fun character who is navigating in a male dominated world (1930's). I love that she is able to keep her femininity while trying to be fearless.

I want to thank the author and publisher for providing an e-ARC via Netgalley. This does not affect my opinion regarding the book.

[Farah G · Rating 3 out of 5]

This story centres around an ostensible challenge from James Moriarty to the famed fictional detective Sherlock Holmes that Harriet initially dismisses. Until some strange events make her question her decision...

This is a very enjoyable mystery story with decidedly classic flavour to it. It easily earns 3.5 stars.

I received a free copy of this book from Netgalley in exchange for an honest review

[Kait · Rating 3 out of 5]

Another fun installment in the Sherlock Holmes secretary series! I like how (generally) old-fashioned these stories are, kind of like a BBC production of a young woman trying to make her way in a man’s world. There was a random “love is love” reference that felt completely out of touch with the setting, and I’m personally frustrated by the love triangle developing around the FMC (the right/good choice seems super obvious to me!), but with that cliffhanger I’m definitely eager for the next book!

[Annette · Rating 4 out of 5]

This is book three in this series but can be read as a standalone.
Harry is once again hard at work answering letters to Sherlock Holmes. She finds a letter in the Times addressed to Holmes from Moriarty. All too soon she’s caught up in another mystery.
It’s another good book in this series. I like Harry and her friends. I’m looking forward to what Harry gets caught up in next.