Now that the first two episodes of the Doctor Who spin-off The War Between the Land and the Sea have transmitted on BBC One and IPlayer, here is a primer of what viewers can next expect.

The first two episodes of The War Between the Land and the Sea showed that humanity has underestimated Aquakind. When the two sides met for their summit, amphibian Ambassador Salt (Gugu Mbatha-Raw) rejected humanity’s first choice of ambassador and insisted on dealing only with Barclay Pierre-Dupont (Russell Tovey).

Then Aquakind launched a devastating attack, thrusting all of the plastic humanity has dumped into the ocean back on land, to drive home the impact of what human pollution has had on their habitat.

The Deep:

As the negotiations continue, Barclay prepares to meet Salt in her own domain underwater. What awaits on the terrifying journey beneath the waves as he and the team take a spherical submersible to the Romanche Trench five miles deep?

Meanwhile, back on dry land, Kate Lethbridge-Stewart (Jemma Redgrave) attempts to negotiate with Prime Minister Harry Shaw (Vincent Franklin). Slick warmongers Sir Keith Spears (Patrick Baladi) and General Oscar Gunsberg (Stewart Alexander) attempt to influence Shaw to change the course of the conflict.

The Witch of the Waterfall:

Barclay and Salt go on the run in a war-torn London as UNIT reels from disaster.

As Salt’s fellow Homo Amphibia named Tide (Samuel Oatley) threatens the land and General Gunsberg advances his plans, the Severance plans demand blood.

Written by Pete McTighe and directed by Dylan Holmes Williams, the next two episodes of The War Between the Land and the Sea, will transmit on BBC One and BBC iPlayer in the UK on 14 December 2025. The Deep transmits at 8:30p.m. followed by The Witch of the Waterfall at 9:20pm.