When primary school teacher Gemma goes missing in Manchester, surveillance officers Martin and Stella are tasked with observing the prime suspect, Gemma's boyfriend Greg Sullivan.
Martin witnesses Greg coming to pieces in front of his eyes. But is this a guilty man trying to hide his secrets or a grieving partner on a mission to find Gemma?
Martin goes on a mission to dig deeper into Carl Tuckman's murky past. Could this relate to Gemma's disappearance in the present?
A birthday lunch held in Gemma's honour leads to secrets being exposed and a break for Martin comes from an unexpected source, as his illicit bond with Zoe deepens.
Martin prepares Carl to confront Kate in the hopes of a confession, but the surveillance operation takes an unexpected turn, leading to devastating consequences.
