It might be a friendly invasion, but when hundreds of US Marines arrive at the quiet Cornish town in the summer of 1943, they turn several lives upside down. Bette Tredinnick, footloose and fancy free, embarks on a whirlwind romance with a handsome GI. Her sister, Sarah, is already married, but Hugh's jealous attempts to keep her out of temptation's reach can't prevent Sarah falling for officer Charles Denham. By the time the war is won, both sisters have lost their hearts.