It is summer and terribly hot. Even after the death of his father, Juncker remains in Sandsted and is not doing the best. The body of a local lawyer is found in the park and Juncker begins to investigate. It turns out not only that he knew the dead man, but he also learns more about his father.

His wife, Charlotte, an investigative journalist, receives an anonymous tip that suggests that the terrorist attack in Copenhagen that destroyed the Christmas cheer in Denmark six months ago could have been prevented. Charlotte gets wind of a good story, so she turns to her husband, who was investigating the case. Juncker knows what happened that time, but he doesn't want to help the woman because he feels it could endanger them both.

In the end, Signe, Juncker's former partner, who also took part in the investigation, but unlike Juncker, feels that the truth needs to be uncovered, to help the journalist with the case. Both women start searching and get into dramatic situations.

Pekelne leto loosely follows the first case of the series about Martin Junckersen and Signa Kristiansen Hard Winter.