Each episode saw the well-meaning and optimistic, but naive, clueless, accident-prone tank top-wearing character, Frank Spencer (Michael Crawford), and his highly tolerant but often frustrated wife, Betty (Michele Dotrice), getting into situations that usually spiralled ridiculously out of control, frequently resulting in someone else's nervous breakdown or some unlikely destructive catastrophe. Frequently the viewer would see a scene in which a character who is familiar with Spencer would warn another about him, although he was usually harder to work with than they had feared.

Episodes usually included stunt work performed by Crawford himself, often highly physical, that even today would be unusual in an inexpensive half-hour comedy. With such a denouement in mind, typical plot lines would involve picnics on high cliffs, driving lessons by the sea, household repairs, or a wide variety of new jobs such as motorcycle courier or high-rise window cleaner. The latter stunt really did go wrong when the rigging equipment being used jammed, necessitating a rescue by the Fire Service. One episode saw Michael Crawford hanging from the outside of a small aeroplane.

The wimpish smiling Frank, sporting his trademark beret and Trench Coat, was married to the (apparently normal) Betty (Michele Dotrice) and in later series they had a baby daughter, Jessica, which offered scope for even more slapstick humour. Frank was a gift for impersonators, and for a time it became a cliché that every half-decent impersonator was doing him, particularly his catch phrase "Ooh Betty". One of Frank's catch phrases was a quavering "Ooh... I'm being ha-RASSed!", or occasionally "I've had a lot of ha-RASSments lately" surprisingly most people now use this pronunciation.

Norman Wisdom and Ronnie Barker were the BBC's first choices for the role, however the choice of Crawford proved effective, as many of Frank's mannerisms and turns of phrase were invented by Crawford, and his stunt-performing and singing skills were used also.