The Swinging Sparrow - S5.E19

A secretary finds she is pregnant to her former boss, Alan Booth. With her current boyfriend, she blackmails Booth, who is married, for $10,000. Then Booth is stabbed with a paper knife during an argument with his stepson, who says it was an accident. Later Booth is found stabbed to death in a car park, and four people are under suspicion: the secretary and her boyfriend, her father, and Booth's stepson.