"The Big Day" is the 1012th episode of Casualty and the eighth episode of the 31st series. It was preceded by "Too Much Love Will Kill You" and followed by "Night of the Loving Dead". The episode was directed by Julie Edwards and written by Tom Higgins and Mark Catley.
Robyn announces to Max, Noel and Jacob that her and Glen are getting married today but requests that they keep it quiet. Meanwhile, Elle is startled to find Connie in the on call room getting ready and is even more surprised when she turns up for work just minutes later.
Elsewhere a young couple, Steve and Danni, are driving away from the police station, having visited as a result of Steve's paranoia that someone's out to get him. He gets her to pull over but she insists that no one is after him. At a local flat, a man named Rhys and his son Joel are preparing for a visit by a social worker to see if he's fit to be looking after his son. However, things only get worse when Joel discovers a stash of drugs in a DVD case. As he's pouring it out over the balcony, Rhys tries to get him to stop, resulting in Joel falling off in the process. By unfortunate coincidence, Steve and Danni are driving underneath the balcony at that moment after he made her steer off the road. Joel lands on the windscreen and their car crashes into a nearby parked van.
The paramedics arrive at the scene and discover the small bag of drugs on the floor near the injured. In this time, Danni has fled the scene. Both Steve and Joel are admitted to the ED and Connie takes charge. However, when she's inquiring as to whether Joel has any allergies, she's distracted by Elle looking through the resus window and puts "nil", despite Rhys telling her he didn't know. Dylan takes charge in Steve's treatment, although he also carries out a blood test for Robyn after she faints in cubicles.
Noel, Max and David try to make Glen's time enjoyable and surprise him with a stag do themed visit. Down in the ED, Steve's becoming more temperamental and when Danni announces that she's breaking up with him, he loses it and holds both her and Robyn hostage for a brief period. To get him to let go, Dylan tells him that Robyn's pregnant. Although she initially took it as a joke, Dylan later tells her that she is in fact pregnant. Steve later apologises to Robyn and it's discovered that he has a condition which is causing his mood swings and paranoia. Danni takes him back as they take a moment of relief.
Connie goes to visit Rhys in the relatives' room and gives him the bag of drugs that were found at the scene, assuming that they're something to do with him or his son. She tells him to get rid of them. Back in resus, Elle continues Joel's treatment and administers him with paracetamol upon noticing that he has no allergies going by Connie's notes. However, he has an allergic reaction to the drug and they're forced to save him. Elle goes to speak with Connie in her office, but an argument ensues resulting in her asking both Elle and Jacob to leave her alone.
In the toilets, Rhys goes to flush the drugs down the toilet but gives in to the temptation and takes them instead. He's discovered by Elle after being alerted by a porter and she takes him into resus. Elle suspects that Connie has something to do with him getting his hands on the drugs but doesn't say anything. Robyn and Glen meet again and discuss the fact that they'll have to start making funeral and life insurance policy plans, something which she's reluctant to dwell on. Although Dylan tells her to inform Glen of her pregnancy, she decides not to at the last minute.
Elle once again speaks with Connie and tells her that she'll have to make the incidents official by the end of shift and instructs her to go and be with Grace. She later does this and as she's holding Grace's hand, she feels her move. Grace opens her eyes and Connie is delighted. David visits Glen shortly before the wedding and Glen asks him for a pen and paper, and he assumes it's for his vowes. Robyn gets ready in her wedding dress and arrives at the chapel where the rest of the staff are waiting. She's surprised to see that Glen isn't there, when David enters holding Glen's letter. Robyn reads it and breaks down in tears, discovering that Glen has left.