"You know," Gwen says, tucking a chip into her mouth. "Even if I didn't know that was Ianto, I'd still see a resemblance. I could definitely pick him out of a shoal." She and Jack make a picture, sitting on the edge of the jetty, shoes discarded and feet submerged.

"I think the correct term is a school," Jack says. Ianto huffs in gratitude; he was itching to say the same. Jack smiles in his direction at the sound.

"It's all in the efficiency of movement," Gwen continues. "And in that sardonic smile." She chews a chip. "You're going to say something about the blowhole, aren't you?"

Jack looks unconvincingly affronted. Gwen leans forward.

"You do make a very lovely dolphin," she tells Ianto kindly. "You have a very shapely tail."

Ianto likes his tail. He slaps it against the water at her words, though whether in agreement, objection, or just to say I hear you, he isn't sure. He can hear everything now with eerie precision - Jack wriggling his toes, invertebrates whistling, Gwen explaining the principle themes of Flipper, even with his head under water. He can hear shapes too, which is disconcerting – the deep bass of solid objects, a cacophony of shoaling fish.

"It does suit you," Jack says. "Aquatic is your colour."

Ianto blows bubbles. He can tell Jack is riffing reflexively. There are notes to his voice Ianto has never heard before – tones of distance, of grief, and sharp edges.

"I still don't get the strategic value of a weapon that turns your enemies into sea-going mammals." Gwen munches. "What's it called again?"

"A Rakh-nakh. And it does tend to make people drop their blasters," Jack says. "But it's more like a prank than a weapon. You know, a cracker bangs, everyone jumps, it's funny. But Rakh-nakh bangs, everyone jumps, you turn into a dolphin, it brings the house down."

Ianto swims a little circle, porpoising as he goes. He's not built to keep still any more; he's apt to sink, or get rolled by the current. On the jetty, Jack folds an arm around Gwen, and looks out across the bay. The setting sun is starting to spill into the sea. Ianto swims up underneath them and nudges with his beak against Jack's bare feet. He opens his jaw, and lets Jack touch along his teeth with his toes.

"I've always wanted to swim with dolphins," Gwen says.

"Well, now's your chance," Jack says.

"I'm not swimming in the bay, Jack," she says. "It's full of turds. Sorry," -to Ianto - "But it is. Turds, and rubbish. Dead dogs. Dead people."

Ianto corkscrews away. There are dead people down there. He knows, because he's dumped them - bloody, furtive bundles in the back of the SUV. He could, if he chose, listen along the bottom for the rise of a rib cage, the hollow of a skull. He could turn up his tail and go and see what lives there now.

Instead, he circles near the surface where the water is still sun-warmed. The bay looks black from above, and grim like a swallowing maw. He never dreamed it would be light and green.

Jack is splashing with his feet and calling out to him. Ianto pops his head up, making Gwen giggle.

"Don't dive too deep," Jack tells him. "Or swim off into the horizon. You could change back any minute." Ianto nods, an action which feels very wrong without much of a neck to speak of. Jack seems satisfied, and sits back again.

"I hear being a dolphin is better than drugs," he tells Gwen.

"Perhaps we should have left him in the bathtub."

Ianto rolls belly up, just to see if he can. He feels pale and exposed where the weak sun touches. He thinks of changing back, but it's like dreaming of a foreign country. He can't imagine himself clothed again in skin which can leak, or think how he walks on the land with his joints all jarring. The tide tugs at a chord in him. He's losing himself through osmosis; all the heavy parts are passing out and sinking. He can't remember anger; that belongs to the earth. He can't recall grief, though he's swimming through the salty taste of tears.

Jack is shouting again, and splashing, but his urgency is just so many bubbles in Ianto's ear – until he feels the change come upon him. He pushes for the jetty just before the tail goes, and then his sense of self is clutching like a drowning man, and pulling him under. He throws an arm to the surface, and a strong hand snags him.

They haul him, heavy and gasping, from the green, and beach him on the pier.

"Welcome back," Jack says, and bangs him between the shoulder blades while he coughs up half the bay.

"I kind of wanted to keep you," Gwen confides as she hands him a towel. .

Ianto lets them prop him up between them, and splutters salt-taste from his nose.

"When I go," he tells them, "Don't put me in a vault. Just throw me in the sea."

Jack's grip tightens momentarily on his arm. Between them, they help him stand, and walk back up the pier on legs that feel like someone else's.

"Have we still got that Rakh-nakh?" Gwen asks. "I think I'd like a go."