A young man in a workplace (possibly library) becomes very curious about a customer who always makes a short phone call before going home. The customer never smalltalks, simply snaps something like 'Coming home'.
One day an incident (forgotten) gives the young man the opportunity to visit the customer's home in the latter's absence - using a key, not breaking in. He enters a hallway which has peculiar scratchmarks running all round it at a certain level, as if someone was circling it constantly, clawing. Of course he ventures in, and realises too late the house is guarded by Something Dead - the customer's brief phone call was in the nature of switching off a house alarm.
I think it was a British story but not sure. There was also mention of a ring set with what looks like a yellow fingernail, which I think the customer wears.