Mum takes his temperature. It's high. He's delirious. He mumbles something like it's funny, isn't it, how mercury is deadly and used to save lives. She pats his leg and tells him not to break it, please. Peter won't, because he's had enough experience with that glittering substance to know better.
He wants to break the glass that encases Caspian and put the hot liquid on his tongue. He wants to taste it, he wants to feel it slide tormentingly on his skin.
It's dangerous and he shouldn't do it. He doesn't know if-and-when he'll return, or if this feeling is anything more than primal need.
It isn't any different than a battle, except that lives cannot be lost. It's still dangerous, but High King Peter isn't stupid; he's isn't going to shy away from something for its risk.
He tastes it. After the battle when the thermometers read a thousand degrees and Peter's eyes burn with shame. Caspian's skin is like golden mercury, trembling as it gives way beneath his fingertips. They are no longer kings or princes, just weak knees and sliding mercury skin. Names that are poison by day slip out of desperate lips at night. They both feel the beads of metal-sweat dripping on their skin and it feels amazing. It's probably killing them.
Peter's world turns to eternal diamonds in the sky and behinds his eyes and on their tangled skins. Caspian can't stop whispering about tomorrow and he seems to think that Peter will soon leave him, but Peter only thinks he could never leave him, knows he won't ever leave Caspian.
They've both had more than enough wine. Perhaps Susan will look at him disapprovingly tomorrow for getting drunk but the High King isn't stupid, certainly, he knows when enough is enough.
When Peter returns to England the thermometers read in the negative degrees. It's so cold without Caspian, Peter's like a corpse. The thin blankets don't help, for the mercury has poisoned him. He never thought it could kill him, he thought he knew when to stop it, but he hadn't even noticed the temperature rising until it shot out of the thermometer altogether and dripped on his skin. He hadn't realized until after it froze to his pores that it was killing him, that he would have been better off never having fallen in love with Caspian in the first place.
End note: This entire piece is inspired by a line from Sylvia Plath's The Bell Jar: I opened my fingers a crack, like a child with a secret, and smiled at the silver globe cupped in my palm. If I dropped it, it would break into a million little replicas of itself, and if I pushed them near each other, they would fuse, without a crack, into one whole again.