New Tricks - Series 4 - Ducking and Diving

The discovery of an armoured security van involved in the disappearance of one person and the unsolved murder of another provides the impetus for the team to look into the case again. The van is at the bottom of a lake, and Pullman decides to dive down and investigate. She survives, but a key witness does not, and the team realise that the murderer is close at hand.