The most obvious allusions are to the Bible. One of the allusions is related to baptism. When the narrator flees and runs into the murky lake, he is, in effect, being baptised...his filthy character is now baptised in the filthy lake. Also, his "baptism" causes him to have an epiphany about his and his friends' behaviors. The narrator realizes that he is not as "bad" as he thought he was, if "bad" at all!
Another allusion to the bible is the narrator's car key. When he finds it, it is referred to as the "grail" and it is the narrator's salvation in many ways. When the sun breaks at dawn, the narrator finds it gleaming in the same spot where he dropped it. The key represents the narrator's escape (and his friends' escape) from the horrible night they've endured. Now that the narrator has found the key, he and his friends can finally leave.