Or, sleuthing in Soho with Becky and Max, whose brilliant older brother Potter, presumably studying premed at Harvard, starts popping up around New York. First, Max spots Potter in a hobby shop, then both children glimpse him at the zoo, and after that, arrayed in strange disguises, the two make an after-school project of discovering what Potter is up to. Before long they've traced him to a Broome St. apartment, seen him come and go in flowing cape and fake mustache, heard his end of a sinister phone conversation (""plans. . . high stakes. . . the government. . . a week from Wednesday, if I'm still alive""), and spotted a seedy-looking man (they call him Mr. X) who is watching Potter as closely as they axe and following him wherever he goes. Readers will begin to suspect the truth as soon as Becky and Max (in X's wake) tail Potter to a West Broadway art gallery where he hands over some ""mysterious diagrams."" But that hardly spoils the fun, for Becky simply becomes more and more ingenious in fitting every new development and cryptic conversation into her picture of Potter as a CIA spy. All the loose ends come together on the fateful Wednesday at the triumphant opening of Potter's first art show, and meanwhile Rice puts enough twists and turns on the comic chase to keep readers racing around lower Manhattan with her intrepid investigators.