Sherlock Bones and Dr. Catson are entangled in an arithmetic adventure. They must follow a teasing trail of addition and subtraction-themed maths puzzles, and it`s up to the reader to solve each sum, all in the hope of foiling Professor Moriratty`s evil plan.

This charming maths activity book features `Sherlock`s Secret Solver` magnifying glass which reveals the answer to each puzzle when placed over a moiré area, allowing children to test their numeracy skills again and again.