"Just Do It" is the 985th episode of Casualty and the 24th episode of the 30th series. It was preceded by "Hearts and Flowers" and followed by "Fatal Error - Part One". The episode was directed by David Innes Edwards and written by Dana Fainaru.
With Emma still recovering the following week, Sam and Grace plan to go back to the United States due to their busy work and school schedules. Despite this, Connie wants Grace to stay with her in the UK but Sam isn't convinced. When Grace overhears Connie telling Jacob she doesn't want her, she breaks down in Connie's office and has a panic attack. Sam later calls her a bad mother and that she will be returning with him to New York as Connie's career always comes first.
Elsewhere, Mercedes is threatened into selling drugs by a woman whom she owes money to named Shelle. She goes to a nearby station but is caught in the act by a nearby PC Wilkinson. She is escaping them in a chase when she falls and injures her abdomen ending up in the ED. Big Mac talks to her and threatens to turn her in, as he doesn't care about being a hero anymore. However, Mercedes voices her concerns after she's sent a picture of her son Connor and fears his safety.
Noel buys Big Mac a motorcycle to show his appreciation for saving him the previous month, and Mac reluctantly accepts it. Later in the day, PC Wilkinson talks to Mac outside the ED and tells him that they found traces of Mercedes' DNA at the scene of Noel's attack, and they figure out that's how her and Mac know each other. Noel discovers the truth and tells Mac he's moving out.
Elsewhere in Holby, a father and daughter, Sean and Rosie, are planning to run away to Paris, but their plans are cut short when an incident at the bus station almost gets Rosie run over by a bus. They end up in the ED but it quickly transpires that Rosie is in need of an operation, but she is only permitted to see her father during supervised visits once a week as she lives in social care. When Sean realises they've figured it out, he heads to the roof and Connie has to go up and talk him out of jumping. Also, Zoe and Max organise to go for a drink after work after kissing the previous week but he calls it off shortly after the shift, telling her it was never going to work.
At the end of the day, Connie says goodbye to Grace, but after a talk with Jacob comes to the realisation that she could miss her only chance to keep Grace. They drive to the airport where Sam and Grace had boarded a small plane on a connecting flight to their New York flight. Grace notices Connie drive up outside the window, and the two reunite outside on the runway, with Connie telling her she doesn't want to lose her again.