There's a certain amount of shock and panic, as the sentry was supposed to prevent these sorts of surprises. The girls being molested by their orcish captors  shriek out, possibly because the orcs were now struggling with weapons to engage the interloper. Even the leader, who looked dangerously competent, was caught off guard by your sudden appearance. You've got just a moment of advantage, but perhaps that might be enough...<br/><br/>(You get on surprise action before the orcs go)