When she reached the building all but delirium possessed her.
She had hurried up to the first landing, when a footstep behind drew her attention.

It was a man in mechanic's dress, coming up with head bent, doubtless for some task or other in one of the flats.

Perhaps he was going to Bevis's.

She went forward more slowly, and on the next landing allowed the man to pass her.

Yes, more likely than not he was engaged in packing her lover's furniture.