The XYY Man featured the character of William (or Willie) 'Spider' Scott, a one-time cat-burglar who leaves prison aiming to go straight but finds his talents still to be very much in demand by both the criminal underworld and the British secret service. Scott has an extra "y" chromosome that supposedly gives him a criminal predisposition - although he tries to go straight, he is genetically incapable of doing so.
 
Regular characters included Scott's long-suffering girlfriend Maggie Parsons; British secret service head Fairfax; Detective Sergeant George Bulman, the tenacious policeman who wants nothing more than to see Scott back behind bars; journalist Ray Lynch; gay photographer Bluie Palmer and KGB chief Kransouski.