'Mara Maru' was Errol Flynn's penultimate film for Warner Bros.
Errol Flynn, a salvage operator, is pressured by heavy Raymond Burr into finding a diamond encrusted cross at the bottom of the ocean: it had been in a suitcase of a crew member on a Patrol Boat in WW2 that Flynn had been on, and had sunk. Flynn is paid $10,000 to go to the spot where the boat went down. Others are interested in the cross and want it returned to the church it came from. Flynn's female partner in the business tells him that Burr intends to kill him when he has located it, so he smashes the compass; unable to navigate their way home, he is spared being thrown over the side. He deliberately runs the boat onto some rocks, and his partner and another helper flee with the cross, with Burr in hot pursuit. There is a gun battle at the church involving the police, and after a lot of thought Flynn gives up the £1 million cross, and returns it to the church.