*spoilers*
This bonus seems buggy. I remember doing this mission with a PUG where two of the members didn't even know what infusion was (of course they only told us halfway through the mission, ugh). We charged the Inquisitor and all the other mursaat in the area aggroed... we wiped except for a smart wamo who ran away and resurrected everyone after the dust settled. By the time we were ready to go, the Inquisitor was long gone, so we just attacked the group of mursaat blocking the way. We killed them and suddenly BAM, bonus mission complete and half of the mobs on the way to Markis' keep despawned. WTF yo? Not that I mind, of course.
-- Z.