The hired guide's son accompanies you, he wouldn't want you getting lost in his city. You have been wandering for an hour and a half with no luck when he asks you what you are looking for.
Constantine looks around subtly to make sure nobody else is in earshot. "Well... my aunt sent me here... there are supposed to be wizards in this town. Have you ever heard rumors of that or seen them?"
Constantine slaps his forehead. "Nicea!? I thought you didn't know where we needed to go?" He sighs exasperatedly. "I guess it's not your fault, I should have been more clear. I've been trying to find whatever he was guiding me to, here. That's where my aunt was sending me. I should explain; my mother and my aunt are both Wise Women; I inherited their talent, but they said there's a special place for training men, they can't train me. So I thought it was around town here somewhere, I was trying to find it on my own. But I guess I need to go to Nicea. How do I get there?"
Constantine shrugs. "I know, but maybe I can find the place, if you can get me to the city. I may as well look, and once I have lodging you can go back home; then if your father recovers he can come find me, and if I haven't found it already he can take me there."
[I'm assuming he has enough money for such travelling expenses.]
"Very well, I will take you to Nicea, but if we do not find your people in Nicea, I am out of options." he takes you to an inn where your room has already been arranged, and you leave in the morning. You travel for a full day and arrive in Nicea in the evening where your guide explains "I have a place for myself to sleep tonight, but if we do not find your group, I'm afraid no arrangements have been made for you."
After making sure Trintion is comfortably housed, Constantine goes to bed for the night. In the morning, after breakfast, he casts a spell, and tries to systematically search the city for magic lacunae.
In that case, he will get a portable dinner for himself, and a small sack of oats for Trintion. He sits with the horse in a park or town square and eats, whispering his intended plan. "I'm going to hide us from prying eyes and ears, and search the city during the night for any pockets of magic, hoping we can find the covenant. It's maybe not the best plan, but I don't have any other ideas. Do you?"
Constantine shrugs. "Ah well. Then we will continue with my half-baked plan, then."
Constantine will cast one spell as he eats (the InVi) then find an out-of-the-way spot to make them both invisible unobserved. "We're both going to disappear. I can't ride when I can see you, let alone when I can't, so I will just have touch to detect you with, I'm just going to trust that you're following me by scent, but please don't get too close and step on my feet, ok?" Once invisible, he will spend the night searching for a magical aura, focusing on the oldest areas of the city.