Kevin (Macaulay Culkin) thwarts Harry (Joe Pesci) and Marv's (Daniel Stern's) plan of robbing his house, with a pack of booby traps that work perfectly. He calls 911 and reports a robbery from Mr. Murphy's house, across the street. He then lures them into "trying to catch him before he calls the police". He runs off to the Murphys' house, enters the basement and when he opens the door to the kitchen, he sees, surprised, the burglars were already there waiting for him!
It seems he's doomed; they talk about getting back on him the same way. But then, Marley, the shovel guy (Roberts Blossom) comes in and knocks them both unconscious, thus rescuing Kevin. The police comes along, and takes Harry and Marv away; Marv screams that he wants everyone to know them as "The Wet Bandits".
The next morning, Kate (Catherine O'Hara) finally manages to arrive to the house; she and Kevin both meet and embrace; and just seconds after, the entire family rushes in behind them.
In the end, Marley is seen reconciling with his family, while he and Kevin wave at each other; and then, we hear Buzz (Devin Ratray) screaming: KEVIN!! WHAT DID YOU DO TO MY ROOM???!!!, which makes Kevin run off scared.
Thanks Dr. Mat!