Trace didn't like the prospect of fighting three men at once. Especially when there was one he absolutely couldn't kill, and it was the most dangerous one of the set.
If he accidentally killed Martin, there would be no chance of freeing the prisoners trapped behind walls of thick rock.
But clearly, from the bickering with the other guards, Martin had at least some inkling of how to use his power in battle. One wrong move could send Trace flying into a wall or crushed by a section of ceiling.
This was a gross disadvantage for him.
So, as he'd leaned around the corner and taken stock of the situation, he'd made two decisions.
Firstly, melee combat in this confined area would not end in his favor.
Secondly, Martin had to be taken out first, but not in any way that would impede rescue. The other two were inconsequential, comparatively speaking.