Asleep in the Deep (S05E01)

A bomb has damaged the pumping station at the reservoir, leaving Walker and Godfrey trapped inside. Hodges is set on blocking Mainwaring's rescue efforts until they realize the building's structure is dangerously unstable. They decide to draw lots to determine who will go in and rescue the two men. Once they manage to reach Walker and Godfrey, disaster strikes as the roof collapses, trapping everyone except Jones in the flooded underground bunker. As water rises, Godfrey finds himself with an unexpected solution that could prove more effective than simply asking for help.