Tom Brennan is a doctor in Kate's hometown in Iowa. He and Kate grew up together, and as children, they expected that they would be married when they grew up. He is married to Rachael, and they have a baby, Connor. Tom was shot to death when Kate tried to escape from the police in his car.

Diane, Kate's mother, is in the hospital seeking cancer treatement. It is apparently not going well. Kate returns to Iowa because Diane is dying, setting into motion the events surrounding Tom's death.

Sun poisoned the water in an attempt to keep Jin on the island. Michael accidentally drank the water and became sick. Sun admitted to Jack she poisoned the water, but didn't tell him it was Kate's idea.