Okay, so the overall plot is fine. It's a pretty simple story, there's a significant lack of detail, of the locations and of the characters, that it makes things hard to follow. This may be a result of tis being a script for you alone to follow, but then again you are the one asking for feedback.
I'll tell you this, it's not very scary if that was one of your goals. Like in concept, this idea of spider people is pretty freaky, but aside from that, I don't get the fear or horror that would come from a scary story. The main reason for this, I think, is because were' not getting much from the characters in terms of dialogue or emotional decriptions.
Things are happening one after another with out pause; there's no flow. We don't get a brief moment of reflection until the very end of the story after all is said and done. And yes, the story may be short, but that doesn't give it an excuse to be rushed.
The two main characters, Penelope (Penny) and Carter don't really have personalities. You could argue that Carter is the coward and that Penny is the brave one, but there snisn't much supporting that other than Penny used a makeshift blowtorch and Carter ran away at some point in the story (but does that count since he ran into danger?)
Dialogue... 'Eh' is a I really have to say. It's servicable and surface level. And there isn't much else that I can say except that.