The Intruder (1972)

Arnold Haithwaite is a sand pilot. He pursues his strange and solitary profession on the sands of Cumbria, beside the Irish Sea. A sand pilot, like a sea pilot, must know his way about; he must have a strong sense of locality and identity. But now another figure haunts this strange landscape: a sinister intruder who claims to be the real Arnold Haithwaite.