If you like puzzle mysteries such as The Westing Game (which, by the way, is still great as an adult), you are the target audience for The Twyford Code. It would also appeal to fans of Golden Age mysteries, despite being set in the present. I tracked this down after seeing it described repeatedly as ingenious. Who could resist?
If you’re undecided on this one, don’t be put off by the fact that it’s written entirely in audio transcriptions. I thought that would be distracting and gimmicky, but it worked. The transcriptions were recorded on an old iPhone by Steven "Smithy" Smith, who has just gotten out of prison. He’s come back to his hometown to investigate an event from his childhood, where a beloved teacher disappeared on a school field trip. That story gets intertwined with a children’s author who allegedly put secret codes into her books during World War II, the plan-gone-wrong that led to Smithy’s imprisonment, and Smithy’s adventures trying to track down the truth behind it all. He’s recording his progress for someone named Maxine…and that’s all I’m going to tell you so that I don’t ruin it.
Publishers Weekly sums it up beautifully:
Rumors of the audacious Operation Fish meant to move British gold bullion across the Atlantic during WWII blend with an account of one of Smithy's most daunting heists and converge on a mind-boggling resolution that contains several bombshell revelations. Filled with numerous clues, acrostics, and red herrings, this thrilling scavenger hunt for the truth is delightfully deceptive and thoroughly immersive.
I never stay up past my bedtime to finish a book, but the ending of this was so full of reveals that I could not put it down. This was a one-of-a-kind reading experience.