Desmond wakes with a start. The timer is going off. He punches in the numbers and hears Kelvin singing from below. He goes under the floor and finds Kelvin with a key next to a container that says Security System. Kelvin tells him that he could end it. That if he turned the key it would all be over.
After being there for three years, Desmond asks to go outside, but Kelvin doesn't let him. He teaches Desmond how to create a fake lockdown and Kelvin draws a map on the blast door. The work was originally done by Rasinski, Kelvin's partner who put a shotgun in his mouth and killed himself.
Kelvin goes out and Desmond notices a rip in his suit. He follows Kelvin and sees him take off his mask and suit when he's outside. He follows him to the beach, where he sees his boat. Kelvin says he's surprised Desmond had the stones to follow him. The two argue and wrestle and Kelvin hits his head and dies. Desmond hurries back to the hatch, but it's too late to put in the code. The hatch shakes and a voice says System Failure. He tries over and over again to type in the numbers, and it finally accepts them and the shaking stops.
Desmond opens his book and a letter falls out. It's from Penny and it says that all you need to survive is one person who loves you and he has her. She will wait for him. He hears Locke banging on the hatch door, and believing he is the replacement, shines the light up the hatch.