A horseman did not fit that theory anywhere.

That particular horseman had come there deliberately, had given the house a deliberate search, and had left in haste when he had finished.

Whether he had failed or succeeded in finding what he wanted, he had left.

He had not searched the stables, unless he had done that before coming into the house.

He had not forced his way into her room, probably because he did not want to leave behind him the evidence of his visit which the door would have given, or because he feared to disturb the contents of Jean's room.
Jean stared up in the dark and puzzled long over the identity of that man, and his errand.