In the series finale, 50/50 reaches an important milestone as the publishing company branches out into fiction. Erica begins to experience headaches and visions as her training comes to an end and she realizes that she is becoming a fully-fledged doctor who can time travel at will.

Erica revisits her family's 1992 Purim party after she receives an unwelcome birthday surprise from Julianne.

Erica has relationship fantasies on Dave and Ivan's wedding day.

Julianne and Brent continue to hide their affair, while a visit from an unexpected person from Erica's future may shed some light on what the future may hold for her. Dr. Tom, on the other hand, isn't allowed to divulge the nature of his work to Amanda, which may place a wedge between the two.

Erica bonds with Ethan in both the past and the present; Julianne and Brent share a revelation.

Dr. Tom grants Erica limited time-travel powers as part of her training and she is tempted to use them to resolve her arguments with Adam before they can get out of hand.

Dr Naadiah realises that Doctor Tom is repeating his old patterns of behavior outside the office and she encourages him to return his ex-fiancée Amanda's calls.

Erica revisits her high-school days to help an exchange student; Brent doesn't jive well with the new River Rock.

Sam and Erica's mother and father host a lunch for Lenin's parents to celebrate the baby news, but Barb doesn't seem to be taking it well and makes the event uncomfortable for everyone. In an effort to find out what's behind Barb's reaction, Doctor Tom sends Erica back to 1969, when her mother was a 17-year-old high school student.

Erica tries to delve into Julianne's bullying nature while a new assistant tries to adapt at 50/50 Press.

In the opening episode of the fourth series, trainee doctor Erica discovers that her first patient is Josh, who is about to sign his divorce papers after splitting up with her sister. Erica doesn't think that she can help Josh move forward because she dislikes him, so Doctor Tom tries to help her by getting to the root of her antipathy.