"Heads Together" is the 546th episode of Casualty and the 4th episode of the 21st series. It was preceded by "Waste of Space" and followed by "Sons and Lovers". The episode was directed by Rhys Powers and written by Joy Wilkinson.
Selena and Nathan are back together, but she wants to keep it from her colleagues. Nathan tries to undermine Harry by offering him a position which he would share with Selena. This plan backfires when it brings the friends closer together, which makes Nathan jealous. Meanwhile, a new no-smoking policy on hospital premises for staff puts Kelsey in a bad mood. She cheers up when Alice has an idea for a staff game. Elsewhere, the rota for the paramedics has been changed behind Josh's back so that Dixie and Cyd are back in a team together. Josh is unimpressed by the effort to undermine him and partners Cyd with himself. Over the course of the day the relationship between Dixie and Josh improves, and this gives Cyd and Greg a chance to talk as well.