This play actually has a stage direction in it which states, "What happens next isn't very clear." So take that whimsy for what you will. The Hostage is a strong voice piece, but outside the context of the time in which it was written, the political situation being hashed out doesn't resonate too strongly with me as a reader, and so I feel something is lost in the final impact of its negative message about war and enmity.
Set in an Irish brothel that serves as a one-night jail to a charming British soldier, The Hostage does have a lot of fun with its characters and their allegiances. Anybody might be some sort of UK spy, and songs abound to disprove that. What can;'t be shaken, though, is the fact that the soldier will be executed by IRA forces come dawn. And the crew that runs and resides in the brothel comes to like the boy quite a lot. So will they allow him to die or save his life before morning?
That synopsis makes the play a little clearer than it actually plays onstage. The production I saw of this play (after having read it) was winning and pointed up the drama of the situation as best it could. But Behan has a tendency to wander pointlessly from character to character without tying them into the main action, and he also throws in a lot of singing of what I imagine are old Irish politico tunes (as well as just plain folksy songs), and none of that can really mean much to a modern audience/reader. Nor can a reader grasp what's motivating the characters because the world remains half-finished. We are expected to know the reasons for the political divide across the UK, and if we don't, we lose something in the final tragedy of the play. So while fun and frolicking, and dangerous and melancholy, I can't say The Hostage wants to let the other shoe drop, and so it ends up being an unsatisfying read (though a completely fine and watchable entertainment).