The Master has decked the Valiant out in honour of Christmas. The open centre room in which the Doctor sleeps, and the Master himself practically lives, rings with Jingle Bells, which is well on its way to becoming the Master's new favourite song. Best of all, the Doctor's young and handsome again, the Master's Christmas present to him.

The Doctor was rather surprised when the Master showed interest in human customs, but more than willing to explain. After all, Earth is the Doctor's pet subject, and he loves to talk. He explains about Saint Nicholas and stockings and mistletoe, launching into an enthusiastic explanation of the traditions surrounding the latter.

Mistletoe is the sort of vine-ish plant clumped in trees, the Doctor explains. It's traditionally hung above doorways during Christmas, and people who meet under it are expected to kiss. The custom comes from Scandinavia, where it represented peace – enemies meeting under it might declare a truce, or fighting lovers kiss and make up.

Mistletoe is a parasite that clings to a tree, sinking its roots into its victim. The tree grows stunted and struggles to survive, but it rarely dies. The mistletoe can't afford to kill it. A parasite can't survive without its host.

The Doctor and the Master both know this. The Master might never have heard of the custom, but he knows the plant. This is biology. They both know this, so the Doctor doesn't need to say it.

The Master smiles warmly at him. He loves the parallel that the Doctor presents. Tomorrow, there's mistletoe strung around the Valiant.

"Isn't it beautiful?" asks the Master, grinning like a madman at the Doctor.

"Beautiful," the Doctor agrees.

The Master leads the Doctor over the the doorway, under the mistletoe, and leans towards him. He presses his lips to the Doctor's, gently, grinning at him. When the Doctor doesn't protest, he pulls him into an embrace and kisses him properly

And the Doctor doesn't dare to push him away, doesn't dare to fight back. He tells himself that all this won't have happened, so he isn't really standing here shaking, the Master isn't really kissing him . . .

But by the time it hasn't happened, the mistletoe has gone brown and died, and the Doctor is crying over the Master's pyre, and the Master has never ordered the mistletoe picked. It's out there somewhere, its weakened tree turning orange with autumn.