"Not mages as you know them, exactly. I am a judge of the Order of Judges, which is not present in this city or this world. I can verify the truth of statements made to me, either in a context where someone is in my custody or by extracting a clear promise to be truthful. I can also determine appropriate and effective punishments that will be effective at discouraging further misconduct, including distinguishing offenders who are unlikely to stop short of death from others, and calm and intimidate suspect and unruly groups of people. This makes me unusually good at many tasks needed for securing peace and justice in the community, and I am told that you are the person I'd need to speak to about continuing that role here."
For the sentencing, it's more difficult to use, and especially to calibrate, without a specific crime. If I were to sit in on a trial, that would both be easier to demonstrate, and allow the presiding judges to assess it's usefulness. In honesty, that gift is the one I expect to mesh least well with your judicial system."
"Generally, it's applied to prisoners already in custody; they are informed that a specific judge is now responsible for them, and once they are aware, that judge's truth sense applies. Refusing the oath for a specific matter is treated as evidence of complicity, so it's mostly come up with those already in jail or acting as witnesses in other matters in exchange for lenience. I'd be interested in investigating the limits."
"Yes, that's fair. We're the backbone of the justice system in most of the known world, there, so it's hardly strange magic. I'm not expecting it to be quite as smooth here."
"No, on that count it's fine. There have been occasional cases of the suspect not knowing that the promise was made to a judge, and it stayed effective."
"All right. That would be a reasonably good opportunity to demonstrate the sentence-giving, as well."
"I don't need to do it immediately at all; I could do it for several prisoners, and then relate my finding in the next room afterwards."
"Is there a particular time I should return tomorrow?"
Well, let's walk back to the compound, tell the person at the gate there will be a messenger, and then he should probably tell Kaja, too, if he can find her.
Kaja is doing swordstaff routines with some of her fellow paladins in the training yard. Apparently she can interrupt this to go see what Theod has to say when she spots him.
"Hi, Kaja. There's likely to be a messenger for you this afternoon. The mayor's office didn't let me demonstrate, and wanted your word for it first."
"Oh. All right, I can give them a sealed note. What in particular do they want me to verify?"
"The truth sense. I impressed him a bit already, but he's a politician and probably testy about his secrets."
"...He may just be worried that you're some kind of dark mage," she points out. "Paladins are immune to a lot of forms of darkness, so if I say you're all right that's another matter."
"That's probably more fair. Politicians always leave a bad taste in my mouth, so I'm probably being uncharitable."