You're going to look pretty silly delivering up a 16-year-old girl as a master spy.
As he continued to expand his horizons beyond the horror field, gimmick-happy producer/director William Castle turned to the budding spy genre with 1963's 13 Frightened Girls, in which an American diplomat's 16-year-old daughter (newcomer Kathy Dunn) spends her vacation playing spy in order to save the job of an agent (top-billed Murray Hamilton) in her father's employ. She has romanticized his life all out of proportion, so it probably goes without saying that she is totally hung up on him despite the fact that he's engaged to his top codebreaker (Joyce Taylor) and that Dunn's diplomat father (Hugh Marlowe) would likely have some objections to the match. As for the spying business, it all starts out innocuously enough, but it isn't long before Kitten (as she signs her anonymous messages) is being sought after by every intelligence agency in the world, and not because they want to shake her paw.
Castle and screenwriter Robert Dillon (who also worked on the script for Roger Corman's X: The Man with the X-Ray Eyes the same year) have some fun playing around with spy thriller conventions (sample dialogue: "I want a drink." "Of course. What?" "Ginger ale.") and they build up a certain amount of suspense in the scenes set at the Chinese Embassy, where Dunn visits friend Lynne Sue Moon, whose uncle is played by Khigh Dhiegh of The Manchurian Candidate fame. The tone varies too wildly between lighthearted fun and deadly seriousness, though, for the film to be a complete success and the title, by the way, is a complete misnomer. Sure, there are 13 girls (all of them daughters of ambassadors and diplomats) at Miss Pittford's Academy for Young Ladies, but there's only one scene where all of them are frightened at the same time and it's over before the opening credits even start. Look, it's okay if you don't want to make a horror film, Bill, but you shouldn't try to pass it off as one.