Episode 4x1, The Beginning of the End
Desmond returns to the beach and wants to hurry and go find Jack to warn him that the people on the freighter are not who they say they are. He also has to tell them of Charlie's death.Episode 4x3, The Economist
Juliet goes to the beach to get Desmond. Desmond tries to get information out of Frank about who hired them and if it was Penny. Desmond leaves on the helicopter.Episode 4x5, The Constant
Sayid tries to calm Desmond when Desmond unbuckles in the helicopter. After they land, he talks Frank into letting him call the island and then gets the phone to Desmond so that Daniel can talk to him.Sayid, Desmond, and George Minkowski break out of sick bay and make it to the radio room, where Sayid fixes the phone and Desmond is able to talk to Penny.
Episode 4x7, Ji Yeon
Desmond and Sayid are being held in a room in the freighter, where they receive a note that says not to trust the captain. Ray comes to take them to the captain, but when they go on deck, Desmond sees Regina, covered in heavy chains, jump from the boat. He is horrified that no one will help her.Captain Gault tells them that some of his crew are suffering from a sort of cabin fever. He also tells them that he works for Charles Widmore and they are trying to find Ben because he faked the Flight 815 plane wreckage.
Episode 4x8, Meet Kevin Johnson
Desmond goes with Sayid to confront Michael.Episode 4x11, Cabin Fever
Desmond sees that the men they are bringing off the helicopter are hurt worse than what a gunshot wound would do.When Sayid gets the raft to go get survivors to bring them back to the freighter, Desmond says he can't go. He was on that island for three years and he's never setting foot on it again, not with Penny coming.
Desmond watches as Keamy kills the doctor and then the captain in order to get Frank to fly him and his men to the island.
Episode 4x12, There's No Place Like Home Part 1
On the freighter, Desmond tries to find the source of some RF interference so that the boat can be moved to the island. He opens a room to find that the freighter is rigged with C4 explosives.Episode 4x13, There's No Place Like Home Part 2
Desmond tries to decode the wiring to deactivate the explosives while Michael sprays the battery with liquid nitrogen.Desmond can't figure out the wiring and when the light on the bomb turns red, Michael tells Desmond to go. Desmond tries to stop the chopper from landing on the freighter, but it does anyway and he tells them about the bomb.
They put a little fuel into the helicopter, Desmond jumps in with Kate, Hurley, Sayid, Sawyer, Jack, Sun, and Aaron, and they take off, despite Desmond telling them to wait for Jin.
They see the freighter blow up and then they see a bright light and the island disappears. They run out of fuel and crash into the ocean. Frank and Jack get Desmond into a life raft and Jack gives Desmond CPR.
A boat finds them and it turns out to be Penny's boat. She'd tracked Desmond's phone call and was on her way to get him.
When the Oceanic Six leave, Desmond stays with Penny.
