Series premiere. On a regular Tuesday morning, Ruby Richardson is shaken out of her humdrum suburban life when she receives an urgent text that prompts her to fly to New York and board a cross-country train, where she reunites with college ex Billy Johnson. As their adventure begins, Ruby and Billy fight the tension that still exists between them while attempting to root out each other's secrets.

During their first night aboard, Ruby's mind is consumed by sex, while Billy probes for personal details she's reluctant to give up. Comforted by the fact that her husband believes she's on a yoga retreat--and determined to make Billy jealous--Ruby brazenly connects with Derek, a stranger on the train. Meanwhile, Billy works to shake a persistent figure from his past.

Ruby and Billy decide to spend a day in Chicago before making any rash decisions about their next moves. As the two anxiously await check-in at a lavish hotel, Ruby meets an exciting woman at a department store, while Billy tries to handle a relentless Fiona. Later, Billy comes clean about what drove him to run.

Back on the train, Ruby seeks guidance from a new friend and gets a wakeup call from home that leaves her shaken. Meanwhile, Billy continues to lie about Fiona, who raises the stakes to get what she wants.

Run centers on Ruby, a woman living a humdrum existence who one day gets a text inviting her to fulfill a youthful pact, promising true love and self-reinvention, by stepping out of her life to take a journey with her oldest flame.

Stranded in the middle of nowhere, Ruby and Billy argue about what to do next. Each affected by the other's desperation, the two must comes together to confront their actions. Meanwhile, Laurel makes a gruesome discovery and receives an eventful visit from Detective Babe Cloud.