After a farewell party for departing flatmate Eleanor, Jo and Chrissy are anxious to find a third girl to share but find cookery student Robin Tripp in the bath instead. Word gets out to landlady Mrs. Mildred Roper that the girls have a man upstairs and she sends husband George to investigate. He meets a prospective flat-mate called Gaby,which is apt as she never stops talking, and insults her by mistaking her for a man. She storms out and the girls are delighted. They want Robin to stay because he is an excellent cook.
With the girls having convinced the Ropers that Robin is gay and therefore it is quite proper for him to share with them, they have a new problem. On the day Robin moves in, Chrissy learns that her mother, who is no liberal, is to pay a visit. The girls try to bluff Robin into moving out temporarily but end up sharing the room with him whilst Chrissy's mother takes her bed.
Jo is anxious to impress new boyfriend David and strong arms Robin into cooking a romantic meal for him. Robin duly obliges and,to make themselves scarce for the couple, he and Chrissy go down to the Ropers' flat to play Monopoly with them. Unfortunately Robin has innocently cooked pork dishes for David, who turns out to be Jewish,so the evening is not strictly kosher.
Whilst Jo visits her family, Chrissy and Robin are left alone in the flat together and Chrissy is alarmed by Robin's libido as he has been reading sex manuals. However, when he and his friend Larry pull and Robin brings the attractive Liz back to the flat, Chrissy starts to feel jealous and scares Liz off by telling her she is carrying Robin's child.
The flat-mates find that the rent money has gone missing and call the police. However,they are so anxious that the Ropers do not find out about the theft that,rather than explain to them what happened,they try to avoid them. Bad plan. George had picked up the rent and had the money all the time.
Robin is due to play for the college in a football game but ends up in bed with a heavy cold,which he has caught from George Roper. The girls do their best to find ways to get him up and about in time for the game,only to find it was an entirely different game to what he expected.
Robin is conned by his friend Larry into looking after a puppy but he has to hide it from George,who operates a No Animals rule, until he can find a new home for it. Chrissy starts sleep-walking and Mildred's birthday is coming up,sending George to panic stations.