A tanker is heading towards the bridge. When it is boarded by the coastguard the crew are discovered to be missing. The only people on board are five youths, drugged and chained. Saga and Martin are assigned to investigate the case.

Four individuals wearing animal masks post a video online claiming responsibility for the tanker Saga and Martin are investigating. Deaths are reported of people eating poisoned food. Are the cases connected?

Saga and Martin continue their hunt for the eco-terrorists, who have realised the police are on their trail.

The hunt is on for the leader of the eco-terrorists, with Saga and Martin hoping to stop any further attacks from happening.

As the investigation moves forward a new group of four, animal head wearing, eco-terrorists post a video online. Saga is having some relationship issues.

A sunken boat containing skeletal remains is found, that appears to be related to the eco-terrorist case. Martin's son is taken into hospital in a serious condition.

A chemical plant is attacked which threatens to contaminate a water source. Saga realises living with a partner is harder than she thought. Martin looks into Saga's past.

Martin visits Jens in prison and seems to be getting to him. As they re-interview witnesses Saga suspects a statement has been tampered with. Laura regains consciousness and remembers what her assailant looks like.

Saga and Martin have a sketch of the suspect, but can they get to them in time to avert 'The Graduation'. Their friendship is placed under strain by Martins inquiry into Saga's past.

It becomes apparent that the case isn't over and Saga and Martin race to prevent another terrorist attack. Saga faces a decision that may destroy her friendship with Martin.