immediate help needed

[BCollie]

Excuse any spelling mistakes, I have a snake wrapped around one hand so I'm typing with the other
I just went into my house to see my foster cat starting at something on the ground. I looked closer and there was my $130 King Snake, tail rattling, striking at the perplexed cat. The cat, thank goodness, did not kill him. She's such a good girl. She probably saved his life, I don't think I would have found him if she hadn't been watching him.
I immediately picked him up and thought "oh my god I left his enclosure open"
Went to check and it was closed. I have no idea HOW he got out, he's been living in there for almost 2 weeks and has tried his hardest to escape, to no avail. He is nowhere near big enough to push the top open.
Help! What do I do?? I'm afraid to put him back in his enclosure for fear of him getting out again