"Reap the Whirlwind - Part One" is the 1036th episode of Casualty and the 32nd episode of the 31st series. It was preceded by "When the Whistle Blows" and followed by "Reap the Whirlwind - Part Two". The episode was directed by Steve Brett and written by Jon Sen. The episode sees the second appearance of Roy Ellisson, portrayed by John Killoran, who was last seen over 18 months earlier in the series 30 episode, "Belief". The episode also marked the much anticipated storyline in which Lily is run over, with the events playing out into part two.
The first day of Cal's planned strike arrives, and while he and his allies set up their picket line, Lily struggles to decide where her loyalties lie. Still willing to side with Sam and help out in the ED, Lily's relationships with her colleagues take a hit. When Sam calls an emergency meeting with the doctors, he requests for one of them to stay and help out. When no-one agrees to help, Sam decides to make up for the staff shortages by covering the shift himself. However, Sam is unaware that Cal has phoned the locum doctor and persuaded her not to come in, in an attempt to make life more difficult for Sam.
Elsewhere in Holby, Roy Ellisson is enjoying watching a football game in the local pub with friends, and his two sons Mickey and Scott. When a black man, Eamonn, stares at them, they all begin to make monkey noises and shouting racial slurs. Outside the pub, a fight between the two parties occurs, leaving Roy seriously injured and Mickey with a head wound. In the ambulance to the ED, Jez notices a Nazi symbol tattooed on Roy's shoulder, and Roy proceeds to tell Jez to get off of him.
Meanwhile, Lily and Duffy treat an elderly patient named Bridget, who's been told by the airline that she couldn't go to Cuba until she'd received a medical examination. They discover traces of ecstasy in her system, but she makes it clear that she doesn't live by the rules and is for once enjoying life. Lily grows increasingly torn through her shift, as to whether she should side with Sam or Cal. Eventually when Sam orders Lily to move Bridget to the corridor, she decides to leave as a protest. Despite this, she makes it clear to Sam that his protest isn't being done for the right reasons anymore.
Gemma takes her numeracy test so she can keep her job, but Iain doesn't welcome her as she would have liked. It transpires that Gemma was the one who created the fake pictures of Alicia and leaked them, because she was jealous that she woke up with Sam. Iain orders her to move out, and Lily takes an unsympathetic outlook, telling Gemma that she can't protect her anymore.
The strike continues outside the hospital, and Lily is disappointed in Cal when she learns that he sent Robyn into the ED to keep an eye out for how things were going. However, Cal is having problems of his own when Ethan and Alicia are failing to take the situation as seriously as he would have hoped. He confronts them, and reveals that he knows that Ethan slept with Alicia whilst he and Alicia were still together.
Meanwhile, Jez digs deeper into the Ellisson's history, particularly how Eamonn seems to know Mickey. Upon speaking with Mickey, Jez learns that he doesn't follow the same beliefs as his father. Mickey also opens up about how he is gay, and that Eamonn is threatening to leak footage of them kissing in a club so Mickey can suffer. However, Jez speaks with Eamonn and convinces him that Mickey is not cut from the same cloth, and he eventually deletes the video. Mickey tells his father of his sexuality, and a furious Roy doesn't acknowledge it as a part of him, and orders him to leave. However, it's not long before he takes a turn for the worse.
Gemma calls Lily, frantic for some help. Gemma has been drinking heavily and driving around the hospital's underground car park in Iain's car. Lily finds her driving around and shouts in an attempt to get her to stop. Walking through the car park, Lily doesn't realise how fast Gemma is travelling, and is struck as she walks out from behind a parked van. Gemma gets out of the car and finds Lily unconscious on the floor with blood pouring from her nose.
The episode was filmed in early January 2017. The following month, Series Producer Erika Hossington revealed in an interview with Digital Spy that someone would get hit by a car in April, but didn't reveal who it was. She also revealed that two episodes in a row would feature two of the main characters; this was later revealed to the "Reap the Whirlwind" episodes, focusing on Cal and Lily.
Upon the episode airing, there was a huge response from fans, as well as articles produced by online media outlets. One of the primary topics that was being covered was the big question of whether Casualty had killed off Lily. At this point, it had already been inadvertently revealed by Crystal Yu that she'd be reprising her role in the 32nd series, and therefore Lily wouldn't be killed off.