A pleasant day cruising on Sydney Harbour as a guest of Mr Graham Lee, the owner of an illegal gambling casino, doesn't quite go to plan. While preparing his cruiser "Gemini" for the outing, Mr Lee discovers an unwanted intruder who, unwittingly, sets off a murder investigation involving Detective Chief Inspector Simon Webster and Detective Sergeant Noel Elliott. Hounded for results by a newly appointed Superintendent, Michael Hayes, Webster and Elliott pursue their line of enquiries while at the same time endeavoring to maintain a cynical watch on the spiteful domestic events unfolding next door to the Webster residence. Despite assistance from his friend and police informer, Ron Lange, and support from Chief Superintendent Paxton, it is only with the intuition of women's logic is Webster finally able to solve the riddle of the Anchor Man.