Stalking is a powerful ability of Shadow wayfollowers. It allows an
assassin to stalk and hunt down a victim of their choice, or the last
person they were fighting. It only works on players and allows the
assassin a rapid, no nonsense following of the victim.
Stalk by itself with no argument will allow the assassin to automatically
attempt to hunt down the last person they were fighting.
See also: help wayfollow, help 'way of the shadows'