On Monday, Mason prepares to attend his mid-attachment meeting with Ethan, but his confidence soon takes a knock when he fails to insert a femoral line. David receives a formal letter from Rosalene demanding that Ollie return home; Rosa urges David to push back. Ethan decides to postpone Mason's meeting when Effie approaches him with concerns about the trial, and informs Mason that a patient has made a complaint about him. Outside, Effie asks Ethan if he would take the risk, but Ethan reminds her that it is purely her decision as she is the one living with cystic fibrosis. Meanwhile, after Dylan refuses to sign Mason off on the femoral line, Mason refuses Rash's offer of help.
The next day, the ED becomes swamped with patients, and Mason uses his intuition to create a temporary office to treat minor injuries. David tells Ollie about the letter, but Ollie is bothered by his father's complacency. Mason treats an elderly woman named Millie and discharges her after diagnosing her with a viral chest infection. However, Mason realises afterwards that he neglected to order a D-dimer test. Pleased with Mason's work, Dylan allows Mason back on majors.
On Wednesday, Effie is rushed into resus with shortness of breath, but Ethan quickly deduces that she is just having a panic attack. In cubicles, Mason treats a drunk woman named Corina, and her HCG test results show that she is pregnant. Mason castigates Corina for her recklessness; Corina expresses her intent to make a complaint and demands another doctor. After a motivational talk from Jacob, Mason apologises to Corina and offers her support when she explains that she was attempting to induce an abortion. Meanwhile, when David feels that Ollie remaining with him will not improve their relationship, Rosa urges David to have a proper conversation with his son. Ethan encourages Effie to go on the trial as he wants her to have a good future.
The following morning, after Corina gives Mason glowing feedback, Ethan signs Mason off on his patient communication skills. David panicks when Ollie announces by text that he is returning to his mother and goes to find him. David catches up with Ollie, and Ollie is overjoyed when David tells him that he wants him to stay. Outside, Mason discovers that Corina has discharged herself and discovers that she is determined to continue drinking. After Millie is readmitted with chest pains, her condition rapidly deteriorates, and she dies. Riddled with guilt, Mason tries to stop a brawl by reception but ends up receiving a punch.
On Friday, Rash confronts Mason after discovering that he did not order a D-dimer for Millie. Mason tries to blame Jade for the error, but he eventually admits his responsibility and claims that he will tell Ethan. At Mason's mid-attachment meeting, Ethan mentions that Rash has expressed concerns regarding Mason's competency, but Mason dismisses Rash's fears as "professional jealousy" and does not tell Ethan about the details of Millie's case.
- Victor Oshin as Mason Reede
- George Rainsford as Ethan Hardy
- Jason Durr as David Hide
- Neet Mohan as Rashid Masum
- William Beck as Dylan Keogh
- Jack Nolan as Will Noble
- Maddy Hill as Ruby Spark
- Tony Marshall as Noel Garcia
- Jacey Sallés as Rosa Cadenas
- Di Botcher as Jan Jenning
- Abigail Hardingham as Effie Laurence
- Shaheen Jafargholi as Marty Kirkby
- Harry Collett as Ollie Hide
- Tafline Steen as Corina Samways
- Ruth Madoc as Millie Faulkner
- Michelle McTernan as Chloe Faulkner
- Wendy Mae Brown as Angela Reede
- When Mason greets his family on Thursday, the reflection in the mirror does not match the rest of the scene. According to the director Matt Hilton, this has been included deliberately to represent the character's emotions.