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.

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.

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.