Only When I Larf is a film with many genres, including crime, suspense, romance and comedy. A group of three people carry out the crimes. Silas (Richard Attenborough) leads the gang and is an experienced confidence man. His girlfriend, Liz (Alexandra Stewart) and his proteg'', Bob (David Hemmings), also help with cons. The movie opens with the gang successfully carrying through a con. However, when Silas' next scheme goes awry, Bob loses trust in his mentor. Bob decides to replace Silas as the leader and as lover to Liz. For Bob's first plan, he sets his sights on tricking a young affluent mogul, Spencer (Nicholas Pennell). While the new lovers are setting their plans, Silas makes one of his own. He partners with Diana (Melissa Stribling), Spencer's assistant, to steal the money before the young deceitful couple reach the rendezvous. This caper goes to show that whoever gets the cash, will not always have the last "larf."