While the Royal Australian Navy evacuates Salamaua in February 1942 ahead of a Japanese invasion, Commander Frank Houghton (Trevor Howard) coerces an old friend, American beachcomber Walter Eckland (Cary Grant), into becoming a coast watcher for the Allies. Houghton escorts Eckland to deserted Matalava Island to watch for Japanese airplanes. To ensure Eckland stays put, Houghton sees to it that his own ship "accidentally" knocks a hole in Eckland's launch while departing, so his only boat is a utility dinghy. To motivate Eckland, Houghton has his crew hide bottles of whisky around the island, rewarding each aircraft sighting (once it is confirmed) with directions to one of the bottles.