TV viewers first met secret agent Callan in a one-off Armchair theatre play A Magnum for Schneider, in which the disgraced former top secret service agent is seconded to a government section devoted to the elimination of undesirables - by whatever means necessary. Callan's was a violent, bleak world where if you didn't kill first they killed you. He was a cold-blooded killer, an outsider - isolated, often in direct conflict with his superior, Hunter, a codename given to all Heads of Section. So successful was the hit man with viewers that author James Mitchell was asked to write a series that went on to become one of the most successful series in British TV history and ran from 1967 through to 1972... This feature film is an expanded rewrite of the first TV episode in which the disgraced former secret service agent David Callan is given an opportunity to redeem himself with one more liquidation. His assignment is to kill a businessman responsible for a number of bombings and gun running, but not everything goes according to plan.