Cassandra Gran is found murdered in her own apartment. The murderer is quickly identified and convicted. One year later, his sister seeks out the former criminal investigator Anton Brekke and asks for help to prove her brother's innocence. Anton is skeptical, because his brother was the perfect perpetrator. It had to be him. Or... did it really have to?

In parallel, Magnus Torp investigates the murder of Sunniva Nylund, the mother of young children. A coincidence leads the two former colleagues on the same path towards a common killer.