Janet, eager to redress the balance in her broken marriage, makes a move on Billy after he has an adverse reaction to the anti-depressants he has been taking.
As John and Emma's affair is revealed to an unsurprised Malcolm, and Janet argues with her husband, who throws curry in her lap, Billy flees to the greenhouse at the bottom of the garden where, unknown to the couple, he has been living for the last few days since walking out on his bereaved mother.
Rain on the Roof was the second play in a proposed series of nine dramas produced by Potter and Kenith Trodd's own production company Pennies From Heaven Ltd. to be broadcast on ITV between 1980 and 1981.
Commissioned by Michael Grade and distributed through London Weekend Television, six of the plays would be written by Potter while the remaining three were to be shared between Jim Allen and an undisclosed writer.
In the event, budget cuts and scheduling problems led to only three plays being produced: Blade on the Feather, Rain on the Roof and Cream in My Coffee.