Mannequin

"Mannequin" was first published in The Saint Magazinein October, 1966. Of the four stories published by the magazine, this is easily the best.
Leone, a low ranking fashion model for a Paris designer is being followed day and night for no apparent reason and it's scaring the daylights out of her. One night after work, in a terrifying scene where she tries to lose the the stranger on her walk home, she finally reaches the safety of her apartment and her watchdog landlady. But while peering out her darkened window at the stree below, she realizes she can no longer seem him when there's a scratching at the door.