The three flatmates plan a party,taking advantage of the fact that the Ropers will be out visiting Mildred's sister and her husband. The evening begins well but turns sour when Liz, whom Robin had previously pursued,takes an interest in Mark,the object of Chrissy's desire - and to cap it all,the Ropers return early.
A group of loud Irishmen are holding sway in the pub,one of whom insults Chrissy. Robin attempts to protest but is made to back down. George,on the other hand,wins the man,Mick's respect for standing up to him over a spilled drink. Robin decides that he will learn self defence and take the man on the next time he sees him. The girls are not sure if this is a good idea.
Chrissy's new boy-friend Ian wants to take her to Brighton for a weekend but Robin discovers from Mildred that Ian is married, causing Chrissy to humiliate Ian in public. However,he appeases her by saying that he is divorced. Then Chrissy is brought face to face with his pregnant wife...
The flatmates throw a party for the Ropers' wedding anniversary and Robin invites a German student, Franz to come along. Unfortunately this sets off George's obsession with the Second World War,leading to a falling-out between the two men. One of a set of cuff-links bought as a present for George also goes missing and ends up in the food.
To allow Jo to go out on a date Chrissy and Robin agree to baby-sit on her behalf for Mr. and Mrs. Randall but Robin is severely disappointed. The colour television has been sent back, the drinks cabinet is locked with no sign of a key and every time he tries to get close to Chrissy the baby starts crying.
Robin has got the results of his cookery exam and he has failed. He considers moving back to Southampton to work for his father and the two girls are far from pleased at the prospect of his slobbish mate Larry taking over his room. Fortunately Robin's father arrives to talk some sense into him.
Larry has moved into the flat but his slovenly ways and habit of nicking the others' food are not exactly endearing him as a house-mate. Then Mildred comes up with an excellent idea. Clear out the attic and let him take it as his room. George was spending too much time up there anyway.
Robin has taken his new girl-friend Angie out on a couple of dates but now he hopes to bring her back to the flat to have his wicked way with her. However,not only is she against sex before marriage but she is also an old school-friend of Chrissy,who takes a very protective attitude towards her.
There is a formal dinner-dance at the firm where Jo and Chrissy work but Chrissy's prospective dance partner has injured himself so Robin, after a few dance lessons from Mildred,becomes her partner instead. He tells people that he is a brain surgeon but ultimately comes unstuck.
There's a mouse loose about the house and, though Larry kills it,Robin wants him to keep quiet about it as the girls are scared of the mouse and Robin can exploit their fear to get closer to Chrissy. George also wants to keep up the pretence that the mouse is still around to ward off a visit from Mildred's family, but it is ultimately Robin who gets trapped.
An anonymous admirer is sending Chrissy flowers and chocolates,which she gives to Mildred. Mildred tries to make George jealous by pretending that in fact she is the one with the secret admirer. An old flame of Chrissy's,who is not the sender but is keen to see her again turns up at the house and is mistaken for Mildred's lover by George.
Whilst Mildred is visiting family George tries to evict the four flat-mates by saying that he needs the flat for his - non-existent - aged mother. The truth is that he wants to turn the existing flat into bed-sits so that he can charge more money from individual tenants but his plan is thwarted when Mildred returns.
When Robin is rushed to hospital during a poker game he asks Chrissy to take his place. This is a very bad idea as she has not got a clue as to how to play and puts the rent money at risk. George steals from Mildred in order to get the stake money to take part in the game and pays the price.