The Mark of the Blue Tattoo — Franklin W. Dixon

Chet Morton's very first day on the job -- driving a Freddy Frost Ice Cream truck -- sends him straight into the deep freeze. Two thugs in ski masks hijack the truck and kidnap Chet! Frank and Joe find him tied up in an empty garage, and the only clue to the identity of his kidnappers is the blue star tattooed on their wrists -- the mark of the Starz. A local street gang.