One (Casualty)

"One" is the thirty-first series finale of the British medical drama television series Casualty and the 1,049th episode of the overall series. The episode is written by Paul Unwin, the show's co-creator, and directed by Jon Sen. It premiered on BBC One and BBC One HD on 29 July 2017. "One" is a fly on the wall episode following an hour in Holby City Hospital's emergency department (ED) with additional focus on sister Lisa "Duffy" Duffin (Cathy Shipton) mentoring two work experience girls and paramedic Jez Andrews (Lloyd Everitt) grieving the death of a baby.

"One" pays homage to Casualty and the National Health Service (NHS); executive producer Oliver Kent stated that it recognises the efforts of the NHS, while actress Amanda Mealing said it showcases the challenges faced by the NHS. Producers began planning "One" in 2016, with an idea of producing a live episode. After this was ruled out due to technical difficulties, Unwin settled on an episode filmed in one take. Crew members questioned whether it would be possible, while there was a mixed response from cast members. Most of the cast were trained in theatre so relied on their training for filming, whereas the crew did not have this luxury and found the experience scary.

Filming took place in early April 2017. Cast rehearsed the script in twelve sections, before piecing the sections together and filming it twice every day. "One" was filmed in one take using one mobile camera, which covered 360-degree shots. 35 radio microphones and 6 booms were hidden into the set, while 26 actors wore body microphones. Multiple methods for capturing film and sound used in regular episodes had to be changed for "One". To capture the entirety of the serial's set, a camera operator was lifted down a 17 feet drop in a harness while recording a scene. The production team wore medical scrubs on-set in case they were caught on camera.

The episode was promoted through promotional trailers, a Twitter hashtag, and a countdown on social media. Within a 28-day period, 6.57 million viewers watched the episode. "One" received a mixed response from viewers and television critics alike. Some viewers criticised the camera movement in the episode, stating that they felt "disoriented" watching it. Alison Graham of the Radio Times called the episode a "bold piece of television" while Jessica Ransom of What's on TV felt the episode highlighted the disorderly nature of an ED. The Daily Telegraph critic Michael Hogan gave the episode a mixed review, opining that although the episode was directed and performed well, the script was poor and "needed some doctoring of its own".