Lambert was an Authorised Firearms Officer and criminal operative within Central Police. He was assigned to the Strategic Firearms Command.
Background
At some point before the events of series 3, Lambert became part of the clandestine organised crime syndicate run by Tommy Hunter, taking his orders from DI Matthew Cottan.
Series 3
Monsters
Lambert is first seen in the South Ferry Station briefing regarding an incoming deployment as part of Operation Damson. He is assigned to the VC4 Team led by Inspector Tracey McAndrew, alongside Constables Bellow and Chapel.
The Process
Lambert is seen alongside PC Karen Black and various other members of the Strategic Firearms Command at South Ferry Station when it is announced by Chief Superintendent Terry Reynolds that PC Rod Kennedy has been found dead.
Negative Pressure
Lambert is one of the members of the SFC who guards PC Hari Bains as he is brought into AC-12 for questioning from HMP Blackthorn.
List
We see Lambert standing behind Steve Arnott when he signed back in the Glock 17 he had signed out from the South Ferry Armoury.
Breach
He is one of the two AFO's who accompany DI Matthew Cottan to arrest DS Steve Arnott at the approved premises of Lindsay Denton. He handcuffs an arrests Arnott and warns him to stop talking.
When DI Matthew Cottan realised his cover has been blown, it is Lambert who helps him escape the AC-12 Building. After receiving a text message from Cottan, Lambert guns down the other AFO guarding the interview room, and then shoots through the glass walls in order to allow Cottan to escape. Before the building can be locked down, Lambert forces an officer in the lobby to let them out at gunpoint. Giving his sidearm to Cottan, the two run down the high street in Kingsgate towards the Moss Heath area where their pick up point is located.
En route to Moss Heath, the two are confronted by an armed DC Kate Fleming, who orders then to drop their weapons. Lambert is the first to respond, turning and aiming at Fleming, but is gunned down by her before he can pull the trigger.