"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.