"THE GREAT CAKE MYSTERY." By Alexander McCall Smith. Anchor Books. 7 and up. $6.99.
For all the fans of Precious Ramotswe, Botswana's No. 1 lady detective -- and there are legions -- and for all the kids who think it would be fun to solve mysteries, "The Great Cake Mystery" delivers a sweet, fun story about how Precious got her start detecting.