In the fifth season, Captains Strand and Vega, along with the 126 team, race into action when in a catastrophic train derailment endangers several lives, including some of their own. With Judd resigning from the 126 to take care of his recently handicapped son Wyatt, Owen must find a new lieutenant to replace Judd and has a difficult decision ahead of him when both Marjan and Paul apply for the promotion. Tommy is ready to take the next step in her relationship, but she finds the road to happiness is filled with obstacles. On his 30th birthday, T.K. gets a surprise visit from someone from his past that could change his and Carlos' lives forever. Now officially husband and husband, T.K. and Carlos' marriage is put to the test when Carlos becomes obsessed with solving his father's murder.