A huge train accident in an idyllic small town shocks the whole of Finland, and accident investigator Marita Kaila is faced with the most difficult case of her career. Under increasing pressure, Marita and her team try to find out what led to the death of dozens of people. But there is also a tragedy in Marita's own past, which the demanding investigation brings to the fore. Will he solve the case before the pressure becomes too much?
Iiris tries to recover from her difficult separation with Artturi when she unexpectedly meets Anton. The relationship doesn't get a chance to progress far when Iiris' son Niilo suddenly becomes ill. Niilo would only need a small operation, but once the boy enters the operating room, the hospital is subjected to a cyber attack. The power is cut off, the ventilators stop working and all access to patient data is blocked. Nurses have to prioritize whose life is the most valuable.