So that they can be together more often, Pierre poisons his sickly wife without anybody suspecting, and Lucienne starts visiting his house at night.

Her husband Paul, aware of the goings-on, blackmails Pierre into supporting a dubious land deal.

Hélène, Lucienne's teenage daughter from a previous relationship, asks for a follow-up investigation to clear her mother of any suspicion.

[4] René Balaire, a heating engineer, was found burned to death in his car, from which his wife Yvette had escaped unharmed.

The police investigation found that he had died from a revolver bullet fired by her lover Bernard Cousty, who had previously killed his own wife.