Perez and his team face a race against time to prevent disaster striking Lerwick. With nowhere left to run, an increasingly desperate killer looks to make a devastating political statement as the current series of crime drama Shetland draws to a close.
Ally and Carol Anne insist their eco-group is non-violent and are stunned when Perez reveals photos of Connor's tortured body. Believing someone in the group is building another bomb, Perez makes Ally see they've been fooled by a person close to them, revealing the identity of the suspected mastermind.
When the police find a suspect truck laden with chemical drums parked in Lerwick town centre, they join forces to corner the bomber before it's too late.
However, when the bomber panics, Perez tracks the increasingly unhinged suspect to the site of the Braer oil spill and a life or death stand-off ensues – putting Perez's future in sharp focus.
As the investigation nears its end, it becomes clear not all the murders are connected, shining a light on a new, unexpected suspect