Dr. Alex Park is a ex-cop who decided to become a doctor. He was a police officer for 15 years before deciding to switch to medicine. He has a cynical personality because he has seen the worst of people. He has a teenage son named Kellan with whom he is estranged. In "Quarantine," Park's son comes for a visit at Christmastime and becomes trapped in the ER when a viral outbreak creates a quarantine. In "Quarantine: Part Two," after Kellan suffers an asthma attack, Park risks his life and his job to break quarantine and help Kellan. Park performs a bone marrow extraction on a father whose regrets regarding his family mirror Park's own. After the man dies of complications, Park reconciles with his son who had helped Shaun save a mother and newborn baby. At the end of the quarantine, Park for once allows himself to become emotional over what he has experienced and accepts comfort from his ex-wife when she arrives to pick up Kellan.