Tom Brennan was Kate's childhood sweetheart. Many years later he had a wife named Rachel, and a baby, Connor. He became a doctor in St. Francis Hospital in Iowa, where he scheduled a fake MRI for Kate's mother Diane Janssen so that Kate could see her one last time before she dies. Following this, Tom was accidentally killed by a stray bullet while driving with Kate who was fleeing the police.
At some point in his youth, Tom accompanied his childhood friend, Kate, to a general store in town. He was in possession of his toy airplane that he received on his first flight by himself. Although intially apprehensive, he served as lookout for Kate while she attempted to steal a lunchbox, but she was later caught. ("The Incident, Part 1")
On the 15th August 1989, he and Kate buried a time capsule. Inside the time capsule were a number of childhood objects, including a red baseball hat and Tom’s favorite toy airplane. They also recorded tape recording, which they would later play in the car. Young Tom and Kate commented on how they will one day be married and have 9 kids.
Reuniting with Kate
In 2002, as Tom left the hospital and got into his car, he was surprised by Kate who was hiding in the back. Kate had been visiting the hospital to visit her dieing mother, Diane. She told him that Diane was dying of cancer, and that she needed his help.
At Tom’s house, Kate looked at Tom's family photos as Tom spoke to someone on the phone about arranging an MRI scan for Kate's mother. After finishing his phone call, Tom talked about his son and wife, and Kate seemed upset at the thought that Tom was with someone. He promised that Diane will get a scan in the next few hours, so they had a little time to kill until then. In the moments that followed, Kate comments about whether “it's still there.” Though Tom was reluctant, Kate insisted that they may never have this opportunity again.
The pair drove out to a bare cattle field, with a huge tree engulfing the landscape. Here, they began to dig up the time capsule they earlier buried. Kate pulled out the box, and inside the time capsule they found a red baseball cap, baseball and Tom’s favorite toy airplane.They also found a tape recording, which they played in the car. Recorded in 1989, young Tom and Kate comment on how they will be married when they find the capsule in the future, and also about running away together. During this, young Kate additionally mentioned that Tom “knows why” she always wants to run. The tape was stopped, and in that moment the two kissed. Pulling away, Kate apologized as Tom said they’d better get to the hospital.
The following day at the hospital, Kate's mother called security when Kate visited her. She ran from the room, but was grabbed by a security guard, whom she dispatched by hitting with him with his own walkie. Tom found her, and the two headed for his car. The police, however, have already created a barricade to prevent her escaping. She shouted for Tom to get out of the car, but when he refused, she drove straight through, clipping the police car and experiencing heavy fire from the sheriff. Though they managed to escape, it is not without cost, as Kate realized that one of the sheriff’s bullets had hit and killed Tom. With little time, Kate was forced to run from the car, leaving both Tom and the toy airplane behind. ("Born to Run")
- Carter Jenkins was the voice of Young Tom on Kate and Tom's tape. ("Born to Run")
- Tanner Maguire played young Tom in "The Incident, Part 1". The casting call described him as "Young Bob, Caucasian. 10 year-old, dark strawberry blonde, or reddish-brownish, blue/green eyes. Cute, nervous about breaking the rules but has an adventurous streak." 
- Tom does not appear for a span of 80 episodes between "Born to Run" and "The Incident, Part 1", the longest of any character.