The Undercover Plan

Tess and Tilly #19

by Kathi Daley

If you love charming small towns, heartwarming relationships, lovable animals, and a touch of murder, you'll love the Tess and Tilly Mystery series set in picturesque White Eagle, Montana.

In Book 19, autumn has arrived in White Eagle, bringing brilliant fall colors, pumpkin patches, and preparations for the town's beloved Halloween Festival. Tess and Tony have once again agreed to chair the annual celebration, and with three-year-old Tommi happily keeping them busy with preschool, dance classes, and plans for her Halloween costume, life has settled into a comfortable rhythm.

That peace is shattered when a controversial newcomer to the community is found murdered on the steps of the historic courthouse, throwing the entire town into turmoil. With leads running dry and pressure mounting, Tesse's brother, Police Chief Mike Thomas, asks Tess to dust off the sleuthing notebook she thought she'd retired for good and go undercover one last time.

As Tony pours his energy into decorating the house, carving pumpkins, and making the Halloween Festival a success, he and Tommi eagerly prepare their family costume for the big night. Meanwhile, Bree decides it's time to tackle the few extra pounds she's accumulated by joining a local gym, Shaggy and Tony begin work on a new game, and Hank receives a letter that has Tess worried.

Genres: Cozy Mystery

147 pages, Kindle Edition

First published September 8, 2026

About the author

Kathi lives with her husband, kids, grandkids, and dogs in beautiful Lake Tahoe. When she isn't writing, Kathi likes to read (preferably at the beach or by the fire), cook (preferably something with chocolate or cheese,) and garden (planting and planning not weeding). She also enjoys spending time on the water when she's not hiking, biking, or snowshoeing, the miles of desolate trails surrounding her home.
Kathi uses the mountain setting in which she lives, along with the animals (wild and domestic) that share her home, as inspiration for her cozy mysteries.

Join me on Facebook at Kathi Daley Books (www.facebook.com/kathidaleybooks) for updates on my books, photos of life in Lake Tahoe, recipes, contests, and giveaways. For weekly updates and contests sign up for The Daley Weekly Newsletter (http://eepurl.com/NRPDf).

Reviews

[Nikki]

Kathi Daley is one of my favourite cozy mystery authors; a prolific writer she has several series which feature strong lead characters who find themselves solving the mysteries they stumble into.

Tess and Tilly is based in the small town of White Eagle, Montana. Tess is a stay at home mum, with one daughter, Tommi. Tess is married to Tony who is a very successful games developer. She used to be the mail person in the town before she settled down. Tilly is Tess's dog who always accompanied her on her mail route, often getting lots of treats from the shop owners along the way; covering leave is no exception, Tilly goes along too. Her brother, Mike, is the police detective in the town.

After a property developer is shot dead, Mike asks Tess to dust off her mail bag and cover the route in the town. This is so she can get infomation about the murder from people who wouldn't necessarily tell the police. Mike arranges the extra leave for the real mail person and Tess resumes her role.

The books are best read in order of publication to preserve continuity of the characters and wider storyline.

I really enjoyed this book and cannot wait to read the next book in December. The books are usually set around holidays, this one was Halloween, the next one is set at Christmas.

[Dorothy Bruce]

Love the Tess and Tilly series

I have read this series for years! This book was great as it blended all the characters from the past and brings in new characters.
As Tess and her family prepare for Halloween it talks about the Halloween Festival, parade and trick or treating. Tony makes some costumes and Tess mom makes some. Lots of fun for the family.
There was a murder among the merchants in the town, and as the story continues several suspects are looked at by the police (Tess’s brother Mike) and in the end the murderer is apprehended.

[Jan Taylor]

Tess and Tilly Ride Again

This is one of my favorite series, and The Undercover Plan does a great job of flying into the future and delivering a new mystery!

This whodunit is full of twists and turns along with some great suspects. it also has a basis near and dear to anyone who has ever lived in a small town: preserving history! I could relate to the emotions the townspeople felt about the proposal to tear down the historic courthouse in the name of “progress.”

This is a great read, so check it out!

[Sheila Penwell]

Love this series, Tess, the amateur sleuth , has been a stay at home Mom since her child was born but on this case, her brother Mike, head of the police dept. asks her to come back to help find clues. Tess takes over her mail route to see what she can find out about the murder of the developer who who wants to buy the old court house property. This is the night of the meeting he is supposed to speak at but doesn't show up. Follow them on their quest to find the murderer. A VERY GOOD COZY SERIES, Awaiting the the next one pertaining to Christmas.

[Marilyn Larkin]

Awesome

So glad to be back with Tess and Tilly and the gang in White Eagle. I have missed visiting with these friends who are some of the first introduction I had to Kathi's books. Of course there is a mystery or two that need solved and Tess helps her brother Mike, the police officer, with solving these mysteries. Can't wait for the next book.

[Cindy]

Good cozy

It is nice to visit with Tess and Tilly. It is now 4 years after the last Tess book. Mike asks her to go undercover by taking over her old mail carrier route. He wants her to talk to merchants following a murder. Tess and Toni have a little girl who is almost 4.

[Millie]

So happy to get caught up with Tess and Tilly and Tony and Titan!!

Life gets busy with children and their activities but Tess still finds time to solve two mysteries! Looking forward to the Christmas story...

[D]

Tess goes undercover to help solve a murder.

It is great to have a new book in this series. Tess is back delivering mail while Toni works on the Hallowen festival. Mike is working on following up on the clues.

[Sally Antoinette]

Back to the old mail run to solve the mystery

What a wonderful story with going undercover back on the mail run. And then it's also Halloween with all the wonderful things going on too. Loved this one!

[Loraina Snowden]

The Undercover Plan: A Tess and Tilly mystery

Another good story in this series. The characters and storytelling is pretty good even though at times there is a lot of repeating in dialogue.

[Stacey Henning]

Tess and Tilly are Back

Now that Tommi is almost 4, Tess and Tilly temporarily take up her mail route to help Mike solve a murder.
I figured out who done it easily, but enjoyed the stories around the suspects who were also considered. A quick comfy read.

[Anne G. Forrester]

A Favorite

As always the Tess & Tilly series is a favorite. I loved the interaction of the families as well as Tess’s involvement with her old mail route to help solve the mystery. Great read.

[Janet Epperson]

Fantastic as always!!

[Susan]

enjoyed the story, nice update with Tess, Tilly and family...

[Debbie]

Tests and Tilly

Just love this series, so glad it has been continued.
I look forward to the next edition due out in November.

[Carola Mac]

Lovely

I missed Tess and Tilly, and I missed Tony who has become one of my favourite characters. I really enjoyed this story I hope there will be more.