The Couple at the Table

You're on your honeymoon at an exclusive couples-only resort. You receive a note warning you to 'Beware of the couple at the table nearest to yours'. At dinner five other couples are present and none of their tables is any nearer than any of the others. It's as if someone has set the scene in order to make the warning note meaningless - but why would anyone do that? You have no idea. You also don't know that you're about to be murdered or that once you're dead all the evidence will suggest that no one there that night could possibly have committed the crime. So who might be trying to warn you? And who might be about to commit the perfect impossible murder?