A Slip-Up bears a number of resemblances to Le Depart (1967), and the reason for this is probably the involvement of Jerzy Skolimowski in the two films. He was director on the latter film, and he has written the screenplay for the former which is directed by Jan Lomnicki.

Following an affair with Marek, a young Warsaw photographer, Helina, a nurse, returns to her husband. However, Marek pursues her, and after having made contact with her at the hospital where she works, he arranges to pick her up there on the following day. To do this, he needs a car, and so he manufactures an elaborate scheme in order to gain possession of one. He had earlier witnessed the death of a child in a road accident, and he re stages the incident with a dummy - the guilt-ridden driver becomes an easy target for blackmail. In his newly-acquired vehicle, Marek sets out to pick up Helina.