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Swept into the bright hustle and bustle of New York, Lily, Robert and Malkin discover shadowy secrets lie beneath its surface. For there are chilling goings-on in their hotel…

A strange boy held captive, haunted by an undersea mystery; and a revengeful villain with a treacherous plan. Searching for clues, Robert and Lily are plunged into deep water… But can they reveal the deadly truth before the secrets submerge them?

Join Lily, Robert and Malkin on a fantastic voyage of terror and triumph, in this fourth Cogheart Adventure.

Audiobook

First published January 5, 2020

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926 people want to read

About the author

Peter Bunzl

13 books332 followers
Peter Bunzl grew up in South London in a rambling Victorian house with three cats, two dogs, one little sister, an antique dealer dad, and an artist mum. As a child he found inspiration visiting TV and film sets, where his mum worked as a costume designer.

After art college and film school, Peter worked as an animator on commercials, pop videos, and two BAFTA-winning children’s TV shows, and wrote and directed several successful short films.

Peter’s debut novel Cogheart was a Waterstones Book of the Month. It was shortlisted for the Waterstones Book Prize and the Branford Boase Award. Moonlocket was shortlisted for the Books Are My Bag Readers Award. Cogheart, Skycircus and Shadowsea were nominated for the Carnegie Medal.

Peter lives in North London with his partner, a fox who visits their garden, and a clutter of house spiders.

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5 stars
249 (38%)
4 stars
232 (35%)
3 stars
134 (20%)
2 stars
22 (3%)
1 star
8 (1%)
Displaying 1 - 30 of 56 reviews
Profile Image for ☾❀Apple✩ Blossom⋆。˚.
970 reviews492 followers
February 4, 2021


I was so surprised when I saw how few reviews this book has on Goodreads. We need to talk more about this series! It really is such a delight to read. This book might be my favourite of all four. It has everything I enjoy in a middle grade book plus the steampunk setting! I absolutely adore it.
Profile Image for Lucy-May.
535 reviews34 followers
September 8, 2020
Middlegrade stories are incredibly important to me & I really wish Peter Bunzl would go on writing this series forever because I completely adore it. Shadowsea was more intense & scary that the other three books in the series & Bunzl very clearly wanted to go out with a bang! I was on the edge of my seat for most of the second half & despite knowing the story would end happily, the writing still ended up making me nervous. I’m so sad this series is over, but it was a fantastic way to end it nonetheless.

⚠️ Death of parents & mild age-appropriate violence ⚠️

Extended Review: https://wp.me/p8MbIo-39L
Profile Image for Milou.
367 reviews9 followers
May 30, 2020
I thought this series was finished after book 3. So I was ever so happy when I found out about this book, and even happier when The Husband found it for me on the airport in Johannesburg for very cheap, with amazingly green sprayed edges. And then I really enjoyed the book as well.

This is a Victorian, steampunk, middle grade series. So all of my favourites really. We follow Lilly, Robert and Malkin, and this time they travel to New York to spent New Year's eve with Robert's mother and sister. In the hotel they meet Dane who asks them for help. This mystery leads them to uncover the mystery of the Shadowsea Underwater Base, and the research Dane's aunt does in bringing things back to life. Yes, we are dealing with zombies in this book...

This is a very bittersweet story. Dane has lost his parents, and this book focuses a lot on how to deal with that. Lilly and Robert have both lost a parent as well, so they are able to guide Dane fairly well on this journey. Although a great friendship is formed, there are still plenty of sad moments, and feelings of guilt for being the one who was saved. All of this has been handled very well.

I loved the new setting, and that we are joined by Robert's sister on this adventure. Kid Wink is a great character as well, and I really liked when one of her primary concerns was getting the police involved and warning Lilly and Robert's parents. The underwater scenes were great, and I adored the scuba diving trip. Also, zombies. Jeey. 

But for some reason I didn't enjoy this book quite as much as the previous ones, and I can't quite pinpoint why. I flew through the first 100 pages, and was kinda sad that I got to go back to work after two months of lockdown. But then it the plot became very predictable, and the mystery not all that mysterious, and it started to drag a bit. 

So I am gathering this is the actual end of the series, and it makes me sad. For one, because I want more. But I also felt that Skycircus had a better conclusion. Our heroes have just arrived in America, and I feel it would be a great start a new part of the series. But alas, this is where we have to say goodbye to Lilly, Robert and Malkin. It was a really fun read I hugely enjoyed.
Profile Image for Melissa Mitchell.
Author 15 books310 followers
May 9, 2020
(4.5/5⭐️) “Even in the darkest places, working together, life could find a way.” A bittersweet end to the amazing Cogheart Series.

In the fourth and final installment of the Cogheart Adventure series, Lily, Robert, and Malkin find themselves in New York for New Years Eve with Lily’s father, John Hartman. Caddy is back for this adventure, too, along with her mother, Selena. When the children receive a plea for help from from a strange boy named Dane and his mouse, they can’t help but rush to discover secrets of his past. Their quest leads them to uncover the mystery of the Shadowsea Underwater Base and a chilling truth. Everyone on the Shadowsea was killed by a reannimation machine by Dane’s aunt—the villain of the story. The bodies were never accounted for and remain there, untouched, rotting. When Dane is kidnapped by his mechanical nurse, things take a turn for the worse, and their adventure leads them deep underwater where Caddy foretells that Dane will awaken the dead at midnight on New Year’s Eve.

This story was bittersweet. I’m rather sad that there won’t be anymore adventures to follow. I’ve grown to love Lily, Robert, and Malkin. But all good stories must come to an end. I found this to be a wonderful conclusion. It was great to see how far the characters have grown.

“Robert had learned that it was the mammoth random things that crashed across your life like tidal waves that made a difference and those were torments no amount of worry could predict.”

Unfortunately, I didn’t enjoy Shadowsea nearly as much as the others. I didn’t feel that it had as much edge-of-your-seat action. Skycircus was my ultimate favorite and felt more suspenseful than Shadowsea, which fell a little flat for me. The story was good, and a little predictable as they all are. That’s one of the things I like about the Cogheart Series. As an adult, I can generally predict what the motivations are, and where the story is headed.

The world Bunzl creates is enchanting. I’ve thoroughly enjoyed getting swept up into stories about airships, mechanicals, and cog hearts. The themes throughout each of his books are wonderful for middle grade readers. The theme throughout Shadowsea was obvious: the ones we love never really leave us even in death.

“The ones we’ve lost, they may be gone from the world, they may be gone from time, but they’re eternal now.”

I thought this theme was great for kids who have lost loved ones. But again, I appreciated the theme in Skycircus more.

It was refreshing getting to have an adventure set in NYC this time around. I loved the Cloudscrapers and Kid Wink, and their cool train car home. Their characters felt very genuine and fit right in with the setting, enriching the pages of the book. And it was fun getting to experience an underwater adventure at the Shadowsea base and, spoiler: zombies!! When the kids donned the scuba gear, I was totally pumped because it felt more unconventional compared to other adventures that kids have in books. One passage especially resonated with me. I felt it was one of the most beautiful passages in the book.

“Lily’s heart soared and she forgot her own predicament as she stared in wonder at the darting glowing fish. She had never seen anything quite so beautiful in all her life. They seemed almost miraculous. There were, she realized, greater things than herself and her friends in the wild corners of the world. Things to whom the water was not a danger, but home. Things that glowed with hope. Even in the darkest places, working together, life could find a way.”

Overall, I loved the story, enjoyed the others more, but am sad the series is over. I subtracted half of a star for what felt like an otherwise perfect story, simply because this story didn’t pack as much of a punch compared to the previous installments. I don’t want to say that I’m disappointed, as it was still engaging and enjoyable, but I guess I expected more out of a finale. I recommend this series at every opportunity. I’ve got friends with kids and I never hesitate to tell them about it. Share it with your kids, or even read it yourself. You’ll enjoy it!!
Profile Image for James Kennedy.
2 reviews
January 13, 2020
An amazing book and a fitting end to a wonderful series! Shadowsea has the usual aspects of the Cogheart world and the fabulous characters are brought to life one final time! I really enjoyed the messages that children will get from this book - the importance of friendship and how to deal with loss and grief. Will miss Lily, Robert... and especially Malkin!
Profile Image for Lauren B.
30 reviews7 followers
December 19, 2019
A fantastic end to a wonderful series of books.
Each book has been action packed as we follow Lily on her journey of discovery and acceptance. She is joined of course by the brave and loyal Robert and the delightful Malkin with his funny quips and one liners.
A must have in school libraries!
Profile Image for Sonal.
26 reviews
May 24, 2020
I have been waiting to read this book for ages . It really exceeded my expectations (and boy , were my expectations sky-high) . It's just as exciting and exhilarating as the other three books , but something about it felt a bit different . It was definitely much scarier than the other three books , with all the 'zombies' chasing after Lily , Robert , Caddy and Dane . The story was quite unpredictable , for example , I didn't know Dane was behind the whole kidnapping and robbery . I also wasnt expecting the death of Miss Buckle. I almost cried . I missed Mrs Rust and the other mechanicals in this book . It just never felt the same , because they were in the other books , and now they were only mentioned . I hope that , after John's speech in New York , Lily and Robert don't get separated . I would like him to go back to Brackenbridge with her , but I'd also like him to be with his ma and sister . It would be nice if both families could be together , perhaps in Brackenbridge . It wouldnt be right to just leave the mechanicals in Brackenbridge Manor while they're in New York . But , whatever happens , happens . All in all , I loved this book , this entire series for that matter . I can wait to read more of Peter's books . And I'm sure they'll be just as good as The Cogheart Adventures . Thank you Peter for making such a great series , and for giving it such a wonderful ending !
This entire review has been hidden because of spoilers.
Profile Image for Laura.
269 reviews
February 18, 2023
The cogheart adventures has been a series I have been interested in for a very long time. I started reading it 6 years ago in my training year for my job as the class I was teaching at the time were studying the victorians. Cogheart became my first ever class book with this group of children.

The series took an unexpected turn, for me personally anyway. I was anticipating that the villain of the story would return multiple times throughout the series. However each novel has a standalone villain. I’m unsure as it stands whether there will be a fifth instalment but I am hopeful as I would love to see a reintroduction of the three main antagonists so far.

Book four made up for the areas I found book three lacking. Whilst some of the issues Lily, Robert and Malkin came across were solved with relative ease, the finale took a bit more determination for them to get the resolve. I’m unsure of if there will be a fifth book at this point but where it has been left there is a definite possibility.

The audiobook for book 3 and 4 are narrated by the same person (different to books 1 &2) and it threw me off a little bit that she does Robert’s voice with an Irish accent as that was not how I imagined it when reading the first two books.


Profile Image for Yogi Pratama.
56 reviews
June 12, 2022
Rate 4.5/5

Setelah sekian lama menunggu buku terjemahannya masuk ke Indonesia, akhirnya penuh antusias membaca lanjutan petualangan Lily, Robert dan Malkin

Sedikit berbeda, karena pada petualangan ini Caddy ikut bergabung menambah kesan ‘mistis’ akibat kemampuan cenayang yang dimilikinya

Namun karena diawal Caddy telah membaca cerita akhir pada petualangan ini dengan bantuan roh, jadi mengurangi greget membaca halaman selanjutnya.

Tapi bolehlah ide ceritanya, issue baru yang belum pernah muncul dari buku-buku sebelumnya, namun sayang ketegangannya tidak dijelaskan secara lebih dramatis. Ceritanya bisa lebih dikembangkan lagi sih soal ‘terjebak di bawah laut’

Tapi secara keseluruhan buku ini bagus untuk dibaca karena membangun imajinasi seperti biasanya.

Kira-kira petualangan selanjutnya tentang apa ya? Tentang pesawat dengan sayap yang saat itu baru dibuat. Mungkinkah?

Peter Bunzl, you did a great job!
2 reviews
April 3, 2020
Shadowsea.
Author: Peter Bunzl.Published by Usborne Publishing Ltd.Published the 9/1/2020

Lily,Lily’s dad,Robert and Malkin go to New York to see Robert’s mum and sister.Little do they know what will happen.This book includes kidnap, stolen precious things and a boy ready to do anything to know what his family was like. In need of help the boy asks Lily and her friends to save him.There are many escaping scenes; old, abandoned train railways, hotel balconies and most extraordinarily underwater, scary places. Lily understands that what keeps the world ticking is love and friendship therefore they must help the boy.

“A gem of a book.”
Katherine Woodfine.

I would definitely give this book a five stars out of five.It really is worth reading it.These cogheart adventure books are my favorite books ever!

Yohan.
Profile Image for diya ✯✯✯.
16 reviews
February 20, 2025
Wow!! What a brilliant ending to this series! This was such a delightful story to end such an amazing series of books. I am a little older than the target audience of this book but felt touched by the literature in the same manner as any 11-14 year old would. Now for the actual book: This was definitely preferable to Skycircus (No. 3/4) and the plot was so much better when it wasn’t Lily or Robert who were in danger, it feels much better for them to be saving someone else! I really enjoyed the plot twist in this book. I am taking away a star because at some points it still felt like Lily’s internal monologue was too mature at times, and also because the story dragged on at points but all in all, I loved it!
Profile Image for Elizabeth P.
507 reviews21 followers
October 16, 2021
I loved the first two books in the series, liked the third one, and this one was simply "okay". It is hard to say what didn't work, but I think some of the situations/actions felt forced.
This rating should probably be 2 stars, but I like Lily, Robert, and Malkin so much that I'm rating it 3 stars. Plus the book does leave you with a warm fuzzy feeling, which is nice. And the book managed to surprise me at times, which can be hard to do in chapter books.

Overall, fans of the series will probably want to read this book. But I wouldn't recommend this book on its own.
Profile Image for The Story Girl.
126 reviews
December 22, 2023
Loved this one! It was a perfect conclusion to the series, one last thrilling adventure.

“People changed too much. They woke up different every day. Learned new things, forgot others. You couldn’t hold on, not really, not to the dead or memories, or the past, or even to your childhood, when you were growing up so fast. But wasn’t that the joy of it? Not the stillness, but the growing. The changing adventure of each day…
To walk a little taller. To see from a higher angle. To grow and change and learn and experience new things – the endless good and bad that shaped your path. And, after all, wasn’t that what being alive was all about?”

4 stars✨
Book 57/?
~The Story Girl
598 reviews
June 3, 2023
I have really enjoyed the Cogheart adventure books and this one was no exception it was very good.

It is a little scarier at the end especially as it is aimed at younger readers but otherwise it was a really fun read.

I loved the authors writing style and the books were so quick and easy to read. They got you into the story really quickly and were a good pace. Malkin the mechanical fox was my favourite character throughout the series and he was done brilliantly.

4 stars - a good ending to the fun set
666 reviews4 followers
August 2, 2020
While I really enjoyed the first couple of books of this series, Shadowsea really let me down. Four books in, Lily is still a very undeveloped character. How does she feel about her mechanical heart? How does she feel about the way other people think of her? I feel like it's hardly ever mentioned.

The ending was also quite bad. It went from being a mystery story to a sort horror story really quickly in a way that didn't suit the previous instalments of the series in the slightest.
94 reviews
October 28, 2021
Wow, this book is absolutely amazing. It is captivating and mysterious from the start. It ends a small mystery at the beginning and reveals maybe a plot twist. I liked the variety of characters, but also that although Caddy was sort of a side character she went with the others as part of the mystery,not just a tag a long. As this is the first book of the series of the series I have read, this has certainly inspired me to read the others. Totally recommend this amazing book!!
This entire review has been hidden because of spoilers.
Profile Image for Emma Reynolds.
359 reviews2 followers
October 28, 2021
I thought this was a great end to the series. It had some twists, plenty of adventure and it was nice to have a new setting.
No real character development in this book fir the main characters but as a book aimed at younger readers, I feel that's totally fine.
The format of the story was similar to the last ones- characters make silly choices, get themselves in real danger/nearly get killed, the baddies get caught and it gets resolved. Overall, enjoyable and great for age 9+
4 reviews
April 22, 2022
This must have been the best book I’ve read all year from year5-6
I adore this author and the secrets and I really like how this books really reminds you and me of friendship and trust. It’s an awsome book to finish this fantastic series and most people say that the 3rd and 4th book of a series are soooo bad, but they really are wrong when they read this series! Highly recommend.
443 reviews2 followers
November 20, 2020
Gänget har kommit till New York, men det märker man tyvärr inte så mycket av eftersom en stor del av handlingen utspelar sig på hotellet som sällskapet bor på. Bitvis seg, men slutet är spännande. Och tänkvärt om liv och död.
Profile Image for Tammie.
830 reviews
January 31, 2021
Read- January 2021
- I was so disappointed in this book. I adored the first few books in the series but these last two just didn't have the same effect on me. I still liked it, just not as much as I wanted to.
Profile Image for Oliver.
7 reviews6 followers
April 14, 2021
An enjoyable adventure involving the fantastical, the supernatural and historical. Fans of fantasy and horror will enjoy this book, with memorable characters and a great sense of mystery and adventure.
45 reviews
October 11, 2022
This book closed the arc of the story of the world Peter Bunzl has created. Towards the end there are some lovely moving passages about loss and change that have really stuck with me. I am going to miss Lily, Robert and Malkin.
Profile Image for Briony2181.
281 reviews1 follower
April 4, 2020
I’m sad this is the last one in the series, I would happily have read many more!
Profile Image for Paula Hale.
225 reviews2 followers
July 19, 2020
A perfect ending to a beautiful series of books about Lily, Robert and Malkin.
Profile Image for Hannah.
89 reviews1 follower
October 1, 2020
Wow!!

Loved this addition of lily, Roberts and malkins adventure!!
Displaying 1 - 30 of 56 reviews

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