The Guard Approaches, and His Clothing Becomes Brighter
This is an essential part of the magic system. When you get close to someone's aura, their clothing—and everything else about them—brightens in color slightly. It's important to show it in this prologue.
Unfortunately, it also shouldn't be there. You see, Vasher should be smart enough to hide his Breath in his clothing, as the book later shows is quite easy to do. He shouldn't have left himself holding any Breath. It's suspicious. If those guards had noticed his aura—or if someone working in the prison had been of the First Heightening—Vasher would have been spotted. It's such an easy fix that he should have thought of it.
The problem is, I felt I needed to establish the way the magic works from the beginning. Having to explain why Vasher didn't make the clothing glow would have been awkward and confusing at this point in the book. So I left this as it is.
However, being who I am, I developed a background for why Vasher did it this way. He left his Breath in, and thought that maybe it would be noticed—but if it was, he knew that the guards would lock him in a cell much closer to Vahr. That would be convenient, as it would ensure that he was much closer to his quarry. Of course, in such a cell, he wouldn't be able to Awaken anything and escape. However, he'd planned for that too. He set a little straw figure outside the prison the night before, with specific Commands instructing it to search through the cells and find him, delivering a set of lock picks.
It was risky—but either way he did it would be risky. He couldn't know for certain that the guards would take him to the area he needed to be in, and even if he had hidden his Breath in his clothing, some prisons have rules in place requiring each prisoner to be stripped, just in case they've done just that. Fortunately, these guards were particularly lazy. Anyway, Vasher's contingency plan wasn't needed, as the guards didn't end up noticing his Breath.