Nardole Locates The Doctor

On Christmas Day in 5343 on the human colony of Mendorax Dellora, The Doctor is mistaken by a servant, Nardole, for a surgeon appointed by River Song to attend to her dying husband, King Hydroflax. River Song, who has not yet met The Doctor's present incarnation, fails to recognise him and increasingly frustrates him with her flirtations with Hydroflax. River Song takes The Doctor aside to discuss the operation he is supposed to be performing she reveals that the Halassi Androvar, the most valuable diamond in the universe, has become lodged in Hydroflax’s brain during a raid on the Halassi vaults and is slowly killing him. River Song wants 'the surgeon' to remove his entire head, considering it the quickest and easiest way to retrieve the diamond.

They are interrupted by Hydroflax who has listened to their conversation. He detaches his head from his mechanical body and orders it to kill them. While River Song defends herself The Doctor grabs Hydroflax's head and threatens to put him in the garbage disposal, creating a stalemate and allowing Ramone, River Song's actual husband, to teleport her, The Doctor and Hydroflax’s head outside of the ship. Believing Nardole to have information about River Song, Hydroflax’s mechanical body decapitates him to use his head as its own.

Although The Doctor is convinced that River Song knows who he is, she denies it. She reveals she purposely crashed Hydroflax’s ship in their location knowing The Doctor would be in the area with a TARDIS. Being unfamiliar with his new regeneration cycle, she has pictures of his first twelve incarnations. Ramone though had only been able to find the TARDIS and not its owner. River Song decides they will just have to borrow the TARDIS instead – revealing that she has done this before. However the TARDIS's safeguards prevent it from taking off when it detects that Hydroflax’s head and body are respectively inside and outside the TARDIS.

River Song

Hearing Nardole calling for help, Ramone is tricked and uploaded into Hydroflax’s body as well. Hydroflax’s head allows his body to locate the TARDIS, and using Ramone, forces its way inside. With Hydroflax’s head and body now both inside the TARDIS the time machine is able to dematerialise and travel to the starship Harmony and Redemption, where River Song requests that the Maître d’, called Flemming, deadlock seal the baggage hold in order to prevent Hydroflax’s body from pursuing them further.

River Song then reveals to The Doctor that rather than return the diamond to the Halassi she intends to sell the diamond to a buyer named Scratch, who has secretly filled the meeting point with members of his own species. After receiving payment, River Song and The Doctor discover that Scratch and his compatriots worship King Hydroflax and are after the diamond in his honour. Despite attempts to hide the bagged head containing the diamond, they are stopped from escaping by Flemming, who was tricked into entering the baggage area by the under-duress Ramone. Flemming has promised Hydroflax’s body an even greater head, the head of The Doctor, and believes that River Song will be the perfect bait to get it.

King Hydroflax

Sensing that Hydroflax's head is beyond recovery and will die imminently, Hydroflax's body destroys it, leaving only the diamond. River Song is asked for the whereabouts of The Doctor, but she explains that although she loves The Doctor they are mistaken in thinking that he loves her enough to find himself with her, as she believes The Doctor to be incapable of falling in love. Seeing the steady gaze and mild smirk on The Doctor's face, River Song now realises he has been with her all along and The Doctor confirms this by saying ‘Hello, Sweetie’.

Being a time traveller, River Song is aware that the starship is about to be crippled by a meteor strike, which she uses as their escape plan, taking the diamond in the process. The Doctor uses Scratch’s universal bank transfer device to overload Hydroflax’s body, before heading to the starship’s bridge. While the starship is crashing, River Song realises that they are heading towards the planet Darillium - home to the Singing Towers mentioned by the future River Song as the place where she spent her final night with The Doctor ("Silence in the Library/Forest of the Dead"). Realising that they’re unable to save the starship, they flee back into the TARDIS, but the impact of the crash knocks River Song unconscious.

After avoiding taking River Song to Darillium for as long as possible to avoid their last date together mentioned by her future self, The Doctor decides to give in to the inevitable. After travelling to the next morning, The Doctor suggests to a man searching for survivors of the crash that he build a restaurant with a view of the Singing Towers, and gives him the diamond to fund its construction. Travelling forwards in time once again, The Doctor books the table on the balcony for Christmas Day in four years’ time. When River Song awakes she is told that The Doctor is waiting for her at their table. Hydroflax’s body, which was pulled from the wreckage and is now peacefully controlled by the heads of Ramone and Nardole, has been put to work as a waiter in the restaurant.

Losing Your Head

The Doctor gives River Song a present; the sonic screwdriver she will use in the library. As the pair admire the Singing Towers, River Song notices The Doctor is crying, something he blames on having wind in his eyes. River Song reveals that her diary is nearly full, and asks whether the stories that this will be their final night together are true, to which The Doctor only responds by saying 'Spoilers'. As he can't bring himself to reveal that this would indeed be their final night together before River Song travels to the Library and meets his Tenth incarnation, resulting in her death.

River Song begs The Doctor to find a way around this event, but he insists there's no way to avoid the end of their times together and refuses to tell River Song the future. They both discuss the fleeting nature of things. Fearful that not much time is left before they part, River Song asks how long a night on Darillium is. Smiling, The Doctor informs her that one night on Darillium lasts for twenty-four years, giving them a long last date.

Overjoyed at this news, River Song once more tells The Doctor ‘I hate you’ which he replies ‘No, you don't’. As the two smile at each other, the words ‘And they both lived happily ever after’ are displayed on-screen. Then little by little, the message dissolves and gets reduced to ‘And they both lived happily’, then only ‘happily’, until all the words are swept away completely.