Four O’Clock on Friday by Philip Storey

'Say--' she smiles 'Pretend you're shopping. Would you care to see something in a nightgown?'

From the back cover teaser: 'The hero is a personnel manager who is married to Celia, his employer. But there is another girl, Patsy, who goes for him - all the way. Patsy gets kicked out of the office but comes back with a small baby that she says is his. So, she moves in the house with the hero and his wife - who, by the way, is a part-lesbian and gets into secret business with Patsy.'