You follow the figure into the first room of the catacombs, and then you catch a better glimpse of him entering the hole where you came in (i.e. the narrow cave passages where you have fought the ghouls). It appears clearer to you now that it's an unarmed human boy and that he's trying to rush out of the catacombs through the caves, probably to make it to the outside.
He moves quite fast, and therefore you had no time to target him with spells right now - but might be possible to do so if you keep following him until he is in the larger caves nearer to the entrance.
What would you like to do:
- attack him (Produce Flame or weapon ranged attacks) as soon as you have enough room
- try to catch him or use some other idea to prevent him from running away
- just follow him stealthy and see what happens
- stop here and let it flee
(I will assume that you do your best to stay alert of dangers, should anything else spring up)