Graham With the Transport Cube

The Doctor and her three travelling companions, Graham O'Brien, Ryan Sinclair and Yasmin Khan, are teleported to Tranquillity Spa via a transportation cube for an all-inclusive stay.

On arrival they are welcomed by their customer host, Hyph3n. As Ryan retrieves a snack from a vending machine, he is infected by a Hopper virus, which The Doctor is able to extract from him. While recovering, he meets a fellow guest, Bella. Meanwhile, a physical breach occurs and guests are instructed to assemble for a muster drill. The Doctor convinces Hyph3n to give her access to the ‘linen cupboard’, which is actually a security room with an armoury, where they meet Kane.

The Doctor becomes suspicious upon discovering that an Ionic Membrane is needed to protect the holiday spa. The creatures that break into the spa start killing guests. Making matters worse, the Hopper virus also found its way into the spa's systems, disabling the transporter and security cameras.

Arriving at Tranquillity Spa

The remaining survivors, the spa's mechanic Nevi, his son Sylas, and an elderly woman, Vilma, meet at the linen cupboard, but Vilma notices her partner, Benni, has gone missing. The Doctor builds a new Ionic Membrane from scratch to banish the creatures. Now safe, Kane identifies the creatures as the local Dregs.

It is revealed that the spa is a ‘Fakeation’, a place designed to look like a vacation but in a fabricated environment. The spa's system, which tracks all the guests, shows Benni outside the spa, so the survivors go out to rescue him. From the vehicle, the group sees the uninhabitable desolation of the orphan planet they are on, Orphan 55.

Hyph3n

Following Benni’s tracker signal the vehicle is caught in a Dreg trap and the Dregs surround it, keeping Benni as a hostage. The group makes a run for a nearby service tunnel, but the Dregs kill Hyph3n and Benni is shot by Kane.

In the underground tunnel, Bella reveals she is Kane's daughter, who the latter neglected in order to build the spa. Bella escapes with Ryan via the transporter while the others are forced to continue further along to the stairs as Dregs swarm into the tunnel. After The Doctor, Graham and Yasmin discover a rusted Russian sign, they deduce that Orphan 55 is actually Earth after it was devastated by global climate change and nuclear war.

With the Dregs closing in Vilma sacrifices herself to give the group more time to escape. Going through a Dreg nest, The Doctor learns that the Dregs are mutated humans that survived the fallout. Kane stays behind to give the group more time to escape.

Graham Relaxes

Back in the spa they discover that Bella has resumed her plan to destroy the spa out of anger toward her mother – having placed explosives around the spa. When they go off the Dregs manage to infiltrate the spa.

As the Dregs attack the spa, Nevi, with the help of his son Sylas, manage to fix the transporter allowing them all to safely evacuate. However, Bella and Kane decide to stay behind to fight off the Dregs.

Back in the TARDIS, The Doctor’s travelling companions despair over Earth's future. The Doctor however, tells them that while this timeline is only a possibility, she cannot promise that it will not come to pass; humanity can either make a positive change or accept their fate and end up like the Dregs.