The Endeavour puts into a slipway in Townsville for inspection and maintenance, and the crew welcomes Diana Parker, the charming new operator for the Minus Five equipment. But there are shocks in store for all as Diana is discovered to be an impostor, and one of the diving crew narrowly escapes death.

The Minus Five team become involved in political intrigue when a defector from a Russian ship asks them for political asylum in Australia. Steve Gabo takes his side, until he learns the Russian is not a refugee, but a thief.