The Hardy Brothers Detective Stories (Digest) - this series received a Digest addition so as not to confuse it with its predecessor, the original series, which officially bears the same name. It was first published in 1979 by Simon & Schuster and existed for more than 25 years, until the beginning of 2005.

Who would have thought that real ninjas could appear in the quiet American town of Bayport! What are they doing here? Is their appearance connected with the mysterious robberies of weapons depots? These and other questions must be resolved by Frank and Joe Hardy as they enter the mysterious world of professional karate.