The German lightship (permanently anchored floating ‘lighthouse’) Borkum Riff is about to be decommissioned. For his last tour of duty, captain Johann Freytag brings along his near-adult, rather estranged son Fred. The ship picks up three men stranded in a broke-down boat. Those prove armed. The captain tries to avoid trouble low-profile, but crew, son and the trio, which turns out to be violent robbers on the run, keep finding out and waving his non-violent advice, leading to repeated bloodshed.