THE UNHOLY NIGHT (aka: GREEN GHOST) is one of the earlier in a long line of "old dark house"-type movies. This time, a thick fog settles over London, and a killer takes advantage of the cover, strangling a number of unwary victims. The scene switches to the obligatory mansion, where a group of soldiers have gathered for a reunion. As often happens in these films, a will is introduced, and a mysterious figure apparently starts murdering them.
It's all fairly enjoyable in a mindless way, but the real highlight is a cameo from Boris Karloff. While his character isn't in it for long, he certainly makes the best of it. He's basically the world's creepiest lawyer. The rest is a silly yarn, but Mr. Karloff is superb...