The door was latched, but not locked.

He opened it and went in.

The building was long, with many stalls ranged side by side.
Wogan's pony stood in the end stall opposite to the door.

Wogan took down the harness from the pegs and began to fix it ready on the pony.

He had just put the collar over its head when he heard a horse stamping in one of the stalls at the other end of the stables.