Wow, thanks for the variety of ideas, everyone! The one consistent recommendation has been Balance of Terror, and I think that the emphasis on action and war will appeal to him. If I'm lucky, I might be able to talk him into round two, which will depend on which mood we're in: Tribbles if lighthearted, Corbomite if more serious and philosophical. Our rendezvous with the Enterprise is set for tomorrow night, and I'll be sure to post the result, in case you should ever find yourselves in a similar bind.
Thanks again for so many excellent ideas - with luck, tomorrow night, a Trekker may be born!