SNEAK ATTACK
An attacker may lie in wait (ambush), attack from behind, or sneak
(Prowl) up on an opponent. If the opponent does not discover the
attacker, then the sneak attack is successful. The sneak attacker always has Initiative, and the defender may not Parry or Dodge the sneak attack.
[Note: I understand this to mean that if the attacker is not
detected before making the first sneak strike (1 melee attack/action),
it auto hits. Any strikes thereafter are obviously detected by the
attacker and require a normal strike roll, although the sneak attacker
retains Initiative while melee attacks/actions are available to them
that combat round. DM]