Alan McKim is the proud owner of Genevieve, a vintage car. His enthusiasm is not shared by his wife, Wendy, but she is prepared to accompany him on the annual London to Brighton vintage car rally, occurring the next day.

Having clashed over his dedication to the car and Wendy's sacrifices, the pair agree to take part as planned; but the arrival of old friend Ambrose with his own car reignites tensions as he makes jibes about Genevieve.

The next morning, both men and their partners set out for Brighton amidst the other rally participants. They make relatively good time but soon both cars are causing problems, causing fresh arguments to flare, and the McKims bear the brunt of the delays, not arriving in Brighton till late - and finding no decent hotel rooms available.

Over dinner, Alan becomes ever more suspicious of Ambrose's motives: it was he who introduced the McKims to each other so had known Wendy longer than Alan has; and his continuing rakish charm and playboy manner begin raising questions as to the nature of their longer acquaintance. Alan brews on the day's arguments whilst tending to Genevieve, but Ambrose's arrival sparks a fresh clash between the pair - and a wager is soon laid, betting the mighty sum of £100 on who can return to London first the following day.

Still bubbling with frustration, if not anger, come morning, the two men make clear their bet and the day's plan to their partners. But the leg back from Brighton to home proves to be even more comically eventful than the journey the previous day!