TARDIS outline on upper arm

You will not believe what the fen mist gave us this morning. We were marching the cart road past the withy beds when the fog thickened and rolled off the river like wet wool, and out of it rose a box. Tall and narrow, painted the blue of a kingfisher's back, with a little lamp on its roof and four windows set in a row like a clerk's ledger. Corporal Vitalis swore it was a shrine. Gaius said it was some trick of the Brigantes. I touched its door and it was warm, the way a loaf is warm.

Then the mist began to pour out from beneath it, curling around our boots, and bubbles rose in the ditch and popped in rings while the air hummed like a lyre string. Every man stepped back. Only the boy Tertius walked forward, and the door opened onto a room far larger than the box, with a stair that spiralled upward into pale light. A voice from inside asked him whether he had a little time to spare. He said he had none to give. The door shut, the box sank into its own vapour, and it was gone, leaving only rings of spiral pressed into the wet grass as if someone had drawn them with a compass.

Tertius came back to camp at dusk with frost on his eyelashes and no clear memory of where he had been, but he carries a copper coin that was not struck in any year I know, and he will not say whose face is on it.

Write to me soon. Tell me whether the mist still rises at Mother's wells.

Your brother, Lucius