The Baseball Card Mystery — Veda Boyd Jones

It is the luckiest day of his life! Sixth grader Sam Morgan buys a shoebox full of baseball cards at a garage sale and discovers some very valuable cards. But he soon finds the special cards are counterfeit. Sam and his neighborhood friends, Matt Landon and Jill Marshall, are determined to find the source of the fakes, and their quest takes them face-to-face with danger!