With his very successful collections *Professor Stewart's Cabinet of Mathematical Curiosities* (2008) and *Professor Stewart's hoard of mathematical treasures* (2010), Ian Stewart has shown to be a master in presenting these books containing an amalgam of puzzles, paradoxes, jokes, anecdotes, and noteworthy mathematical oddities and make these very accessible for a broad readership. Even it one has only 15 minutes of spare time, it is worth reading a couple of pages, and if it happens to be a puzzle, it might keep you busy for a couple of hours. Stewart says he has them in his drawer as snippets of ideas, too limited to work out as a longer stand-alone item. So he may have cleaned up his drawer for his first collection, and because of the success, looked for more of these to fill up his second collection. Either his drawers are bottomless or he may have a constant inflow of these items, but here is volume three of a similar collection.

This third volume however, has a twist. As the title suggests, some of the items are presented as short mystery stories in the style of Sir Arthur Conan Doyle, in which Hemlock Soames and his assistant John Watsup have to solve some mathematically inspired problems. These are presented as extracts from the memoirs or Dr. Watsup. As the regular readers of Stewart's other books will know, he is a very entertaining author of nonfiction, mostly popularizing mathematics. Here he shows his authoring skills by writing these mystery stories where he develops fictional plots and tells them in the form of dialogues. The psychology and idiosyncrasies of Soames and Watsup are so much mirroring the original Holmes and Watson that, besides the proper mathematical mystery, it is already fun to learn how their characters are developed. The two problem solvers even have professor Mogiarty as the equivalent of Conan Doyle's criminal mastermind Moriarty. Soames and Mogiarty meet in a deadly confrontation in a grand finale. I will not unveil more. Read and enjoy!

The mystery stories are mathematical puzzles as we had puzzles in the two previous collections and they are the most striking novelty in this third volume, but they are not the only items. They are interlaced by other puzzles, riddles, items, oddities. All solutions are found at the end of the book. We find some classics like tilings of the plane, towers of Hanoi, Sudoku's, and number theoretical oddities, but we also learn about the V-shaped flights of geese, how to write natural numbers using only the number 1 and mathematical operations in the shortest possible way, the building of Egyptian pyramids, the formation of sand dunes, public key encryption, how mussels grow, how numbers relate to damping of an echo, the arrangement of rowers in the Oxford-Cambridge boat race, and many more.

This is another delightful volume that should not be lacking form the collection of anyone who loves mysteries, mathematics, or puzzles, which is almost anybody. It can be savored in short chunks as snorters, as snacks, or as tidbits, any time of the day or the night.