A mysterious symbol is the key to a murder case in this classic suspense tale by the Edgar Award-winning author.   Gordon Craigie and Department Z--the squad of top-secret detectives within British intelligence--are embroiled in a desperate investigation involving drugs and murder. How will the department uncover who is behind the mark of the crescent? Will they solve the case before the anonymous culprit claims another victim?   The trail starts at the country estate of Greylands, but no one knows where it may lead . . .