Observations on Geometry

by Camilla Sandman

Disclaimer: Characters are the BBC's. I just borrow, being naughtier than it.

Author's Notes: Thanks to Saz for help, nagging and support and Pat Robertson for inspiring it by being an ass. Thank you, Pat. My first threesome is for you.
Set somewhere after Jack appears, but isn't specified when. Probably a bit AU.

II

When he was fifteen, Jack fancied his advanced geometry teacher. She would smile and talk of angles and he would watch the angles of her legs and imagine them wrapped around him. Even then, he liked to watch.

He still remembers what she taught him. Lines, angles, surfaces and solids and all the shapes of the Universe explained, charted, observed. He was never particular to any one kind, for all her urging to specialize. When he got a new teacher the next year, he still fancied, even if Mr. Lekli had different angles. They were still pleasurable.Jack never did learn to specialize.

II

Jack doesn't fancy the TARDIS.

The TARDIS is a rectangle on the outside and all the shapes within, a geometry rebel that likes to drive Jack mad. Always, when he thinks he's figured out the shape of it, it changes and leaves him walking into the wrong rooms and crashing into the wrong surfaces.

Rose looks sympathetic, the Doctor looks amused and Jack just looks.

Rose Tyler. Curvature, cloth tracing the curves of her skin as she walks, the jumper pressing against her breasts, the jeans stretching across her backside. Lips made to be curved into a smile pressed against other lips.

The Doctor. Lines in pleasing composition. Flat stomach, flat chest, straight shoulders wrapped in leather as he walks. Lines across his forehead to trace, long fingers to feel wrapped around skin.

Jack is never sure which shape he's partial to, and when they walk in front of him, hands linked, he likes to think them one together.

II

Rose fancies the Doctor.

It's in the angles of her neck as she tilts her head to look up at the Doctor, in her fingers as she curves them around his wrist, in her lips as she parts them for a wide smile and her body as she straightens it to meet his lines.

It's in the surface of her skin, tiny hairs standing as the Doctor takes her hand and draws a thumb across, following the lines of her bones.

Jack wishes it was his thumb and is still never jealous.

Rose never says anything. She doesn't have to. Geometry doesn't lie.

II

Jack likes to watch.

Rose kisses the Doctor with her eyes open, head tilted upwards, fingers in close-cropped hair, the Doctor's hands on her hips, their bodies parallel lines, the space between them always skin. She tip-toes to reach until the Doctor curves into her shape, his face against her neck, and the shape changes, a half-circle of human and Gallifreyan halves. Dark and gold, but when their hands link, the skin is the same colour, shades of light meeting.

Rose kisses the Doctor and the Doctor kisses her, obeying the laws of attraction between two bodies, a constant of math that adapts, but never dies.

Jack never tells them he's watching and they never ask.

II

Rose likes to kiss.

The first time Rose kisses Jack, her eyes are closed and lips are half parted meeting his, tasting of wind and her and the Doctor and Jack thinks he may be lost. Leaning against the TARDIS wall, the Doctor is watching, saying nothing, arms folded and eyes dark. Watching as Jack lets hands rest on her back, pushing up her jumper to feel skin; watching as she sighs into Jack's kiss and puts a hand on his chest; watching as she arches into Jack's body.

"Doctor," she says and Jack kisses the pulse in her neck as she speaks, as if kissing the sound of the name spoken by her.

"Rose," the Doctor says, and he's still watching, still watching as he walks over, putting his hands on Jack's hands on Rose's back. Tilting her head back, she meets the Doctor's kiss, and Jack knows the taste of him is still on her lips.

Jack can't help but wonder if the Doctor is sharing Rose with him or if Rose is sharing the Doctor.

II

Jack might be becoming partial to triangles.

The first time, Rose is on top, and he watches her move, cheeks flustered, nails scraping across his chest, her back to the Doctor's chest. The Doctor is kissing her neck, hands at her hips, feeling her rhythm, feeling Jack's. When she closes her eyes and gives in to her body's release, it's the Doctor she falls back against and Jack watches them, gold and dark and both so beautiful.

The second time, Rose against the mattress, the Doctor pressing her down, her hands clawing at his shoulder as he lifts her up to meet his body's thrusts and sinks her down again, like tides obeying gravity, Jack just observing. When he finally he sinks down behind the Doctor and lets his hands feel the muscles tense and relax, tense and relax, it's Rose's arms that link across the three and locks Jack against the Doctor.

The third time, Rose lies on her side between them, face nuzzled into the Doctor's neck, one hand on his cheek, one hand in Jack's. Jack moves, she moves, the Doctor moves, the principles of action and reaction across three. When the Doctor lifts his head over Rose's shoulder and kisses Jack, Rose's sigh sounds like absolution and Jack thinks he might be in love. He just doesn't know with who.

The fourth time, Rose straddles him and the Doctor leans into him, kissing Rose over Jack's shoulder, his body hard against Jack's, hers soft and Jack knows it's with both of them.

II

The Doctor loves Rose.

It's in the curve of his body as he lets her sleep against him, in the sighs he makes as he watches and never sleeps, it's in the faint traces of moisture as he kisses her skin and the gentleness of his fingers as he brushes her hair from her face.

It's in the lines of his face as he looks at Jack, and Jack, Jack knows.

The Doctor never says anything. He never has to. Geometry doesn't lie.

II

Jack still hasn't learn to specialize.

They're dancing; Rose and the Doctor, her head on his shoulder, her eyes closed and face peaceful. There is no tune, no song, only the TARDIS flying and the heartbeats between them. Perhaps that is their song, Jack thinks. Perhaps no composer could capture it in simple notes, the maths too complicated.

The Doctor's eyes are open and they meet Jack's, blue in the green light of the TARDIS, holding a sea within them. A faint smile is on the Doctor's lips as he whispers something to Rose and she smiles without opening her eyes.

Jack wishes he was either of them, both of them and he's still not jealous. He could join them and change the angles and shape, but right now, they're beautiful as they are, dark and gold and geometry in skin.

They dance and Jack watches. He always does.

Geometry is still his favourite branch of maths.

FIN