Casualty is set to deliver one of its most tense episodes yet as newcomer Matty Linklater finds himself in serious danger after a training exercise at Holby ED spirals out of control. What is meant to be a controlled simulation quickly becomes a genuine medical crisis, leaving the self-assured junior doctor potentially exposed to a deadly pathogen.

The pressure on Holby has been building for weeks. Following an anonymous report made by Matty, the department was hit with a surprise spot inspection by the CQC. That visit ended badly, and the consequences were severe: a full inspection was ordered, putting the future of the ED under scrutiny.

Determined to prove that the department is ready, Flynn Byron organises a high-stakes training simulation for Matty and fellow resident Dr Kim Chang. To make the scenario as realistic as possible, Dr Grace Clements, a specialist in dangerous pathogens, arrives to play the role of “patient zero” in a mock encephalitis outbreak. The residents are told to treat the exercise exactly as if it were real.

From the start, cracks begin to show.

Matty notices that the PPE is out of date and challenges the rules of the exercise, arguing that the equipment shouldn’t be used. Instead of following protocol, he refuses to secure his protective gear properly, treating the situation with a confidence that borders on complacency. Kim, meanwhile, is already uneasy. She observes that Grace is tachycardic and running a dangerously high temperature, but Grace insists she’s just under the weather and presses on with the simulation.

Then everything changes.

Grace is suddenly overwhelmed by a violent coughing fit, with blood leaking from her nose and eyes. The room shifts from rehearsal to reality in seconds. She admits she may have been exposed to a real pathogen but refuses to reveal details about her work with the Ministry of Defence. The implications are chilling.

Because Matty hasn’t been wearing his PPE correctly, he’s left completely unprotected when Grace’s blood spatters across his face.

Panic sets in immediately. Realising what he’s done, Matty turns to Kim, desperately asking her to help identify Grace’s symptoms and work out what pathogen he may have been exposed to. The exercise is over. This is no longer a drill.

Flynn quickly takes control, instructing the residents on the next steps and trying to stabilise the situation. He explains that the date on the protective gear is only precautionary — but his shock is clear when he discovers that Matty ignored instructions and failed to wear his equipment properly. What was meant to showcase the ED’s readiness now threatens to become proof of a catastrophic lapse in judgement.

Elsewhere, the emotional stakes are just as high.

Dylan admits to Stevie that he was wrong to secretly take Matty’s DNA to confirm his paternity. He reflects bitterly on the years he lost, missing his son’s childhood while being kept in the dark by Matty’s mother. But that regret is about to be overshadowed by something far more frightening.

When Dylan learns that Matty has been exposed to an unidentified pathogen, his world stops. The secret he’s been carrying suddenly feels painfully irrelevant compared to the possibility that he could lose his son before ever truly getting the chance to know him.

The episode leaves viewers with a chilling question: has one reckless decision put Matty’s life in danger — and will Dylan be forced to face the unthinkable before he ever gets to tell his son the truth?