中规中矩版剧透：
Okay, this is what I think happened (SPOILERS SPOILERS SPOILERS!!): Felix and Vera have broken up, and he is lonely. His neighbor, Martin, who is constantly trying to find things to do to avoid his wife Claudia since the accident which has left her paralyzed, discovers the tunnel in his basement and tries to figure out where it goes. This leads him to Felix's house, where after scoping out its street location, Martin decides that the tunnel ends in his neighbor's basement, so he contrives a way to get inside. He pretends to need to make an urgent phone call, and once inside, Martin asks Felix if he has a basement and upon learning that he does, he returns to his own house, where his wife Claudia locks him in their basement.
Martin, realizing that he will die of insulin shock if he doesn't get out, uses a pickaxe on the wall of the tunnel hoping to escape into Felix's basement. Felix hears the pounding of the pickaxe on the wall and is being driven crazy by the noises, which Vera believes is a loose bedroom window shutter banging in the breeze. Felix and Vera make love, but Felix later finds her missing from their bed. He goes to the kitchen, where he hears the voice of Claudia talking to Martin about being discovered by Bruno echoing through the tunnel into his house, but he mistakenly thinks that it is Vera talking to the intruder. He enters the kitchan to find her alone. Vera, naturally, has not heard the voices and doesn't know what Felix is talking about, so she gets angry at his accusations and leaves.
Felix becomes more paranoid by the thought that the man is still in his house, so after the accidental death of Mrs. Meuller (the dog was just running upstairs and her fall WAS an accident), he acquires a gun and goes home where he sees the shadow of an intruder in his attic. He shoots them sight unseen, then in a fit of vengeance, locks up his house so the stranger will die inside and he'll be rid of him once and for all. Felix destroys his alarm system in the event that the intruder gets a door or window open but is too weak to escape, the police will not be summoned.
Felix drives to a spot in the neighborhood to wait while his captive dies, but 2 kids see his drawing of Martin and recognize the man. Felix goes to Martin's house and breaks in, returning the favor, but soon becomes obsessed with Claudia, who (possibly in Felix's mind) resembles Vera. Bruno, a friend of Martin's, is in unrequited love with Claudia, and when they realize someone is in the house, they chase Felix into the basement, where he discovers the tunnel. He follows it and finds Martin, dead, then escapes back into his own house through the hole Martin has started. Wounded in the back by Bruno, Felix has to know who he shot in the attic and he drags himself to the door where he sees through a hole she made trying to escape, Vera lying on the floor, wounded and bleeding to death. She had returned to his house, using her keys to get in, to look for his portrait of her. As Felix watches her, he is shocked to hear her talking to her unborn fetus, which is undoubtedly his child.
另类解读：（有点离谱）
The home of Claudia was a representation of Vera, the basement of the home was a womb (where Martin always was) and the tunnel the birth canal to the "real world" of Felix's home. So starting with the assumption that Felix's home and what happens therein is the "real world" and what happens in Claudia's house is the dream or metaphoric sphere, I took away the following symbology:
Martin was the symbolic unborn child of Felix and Vera who died/will die before he was able to escape the womb and break through into the "real world" of Felix's house (think the first half of the film is the "real" part, and the second half is dreamlike). Vera and Claudia were played by the same woman because after he shot Vera she became "paralyzed" on the floor (symbolized by Claudia in a wheelchair).
The "other man" that Felix was jealous of was represented by Bruno but the "other man" was actually his own unborn child, represented by Martin that he in reality "trapped" in his house when he shot Vera but was metaphorically trapped in the tunnel.
