Congratulations, you rolled a 19. You're able to shadow step and apprehend the Scroll Thief. He will beg you insistently to let him take the scroll and leave Phlan, as the Black Fist are in hot pursuit.

The scroll itself, mysteriously enough, appears to be completely blank. Wonder why that is.

If you ask the thief about it, he'll tell you that there's no time to explain and to "trust him," and that "getting this scroll out of Phlan is the only way to keep the city safe."