This odd attempt to create a sort of naturalistic two-character drama is thus closest to Milligan's first film, "Vapors," being more indebted to early, earnest indie arthouse models than the genre conventions he otherwise tried to graft his unique form of no-budget hysteria onto. So it's offbeat, particularly within his ouevre. However, that means even more than usual, the actors are dependent on their director's weird, garrulous dialogue and his equally off-kilter ideas about human psychology. So this tale of an attractive London woman who takes in a handsome but helpless homeless boy alternates between the dull and the arbitrary.
The actors manage as well as they can with characters undefined in the writing, not to mention scenes that go nowhere, serving no purpose but to pad the runtime until something finally happens. And that "something" is that, out of nowhere (yet somehow predictably), one character turns out to be "evil" and destructive because, apparently, that's the only way Milligan can conceive of that entire gender. Frankly, if the script was going to go in that direction, it should have done so much sooner, which at least would have provided some semblance of plot tension.
While obviously made on the barest of shoestrings--even by Milligan standards--the movie is perhaps most interesting if you try to imagine just who he, or anyone, thought it might be 'for." Did the director somehow manage to impress some very gullible Brit as an auteur? More likely they hoped he was making a sexploitation movie, which the thin story indeed does suggest it will become, but it's terribly chaste, unless you count the hero frequently having his shirt off. (And god knows that's not the toplessness grindhouse viewers were looking for in 1970.) There are several bizarre moments where it's hinted that poor man is made to perform oral sex on the heroine, and of course Milligan suggests this is a thing of indescribable perversity and horror. But that just underlines that the movie is not only prudish, it's downright anti-sex. As for violence, well, there just isn't any.
I'd always been curious to see "Nightbirds," so at least this can now be checked off the bucket list. But if you've seen excerpts, trust me, you've seen enough. It is not a movie that suggests Milligan was wasted on cheesy horror films, but instead confirms that his having to make cheesy horror films was probably the best possible thing for a sensibility whose eccentric neptitude and myopia were doomed to make any less daft material simply tedious.