"Hey coppers, what am I specifically being detained for? My good looks?"
Resort to snark in an attempt to get out of custody.
"You lot set a good friend of mine on fire. Me? I'm just waiting for the boss to give the word. I'll enjoy this, for sure."
analyse the opposing army and note key info: possible strengths/weaknesses, weaponry, mobility, etc.
Strengths: there are a lot of them. Several of them are very large - even bigger than Freddie and Rex. THey have weapons and armor, and they seem in good repair. There are some who are definitely using magic of some kind or another. You can't tell how strong their magic is. But Rex's ring did just explode after that officer told him not to use magic against them, so maybe they have an ability to counteract magical items. They have something like cannons in the background, and at least one thing that looks suspiciously like , and yet somehow not quite exactly like, a trebuchet. (6) Oh. Yes, they also have flying units. a whole squad, circling the area discretely, at enugh of a distance not to be immediately obvious, but close enough to act should things happen.
Also, they did manage to catch your entire group unaware.. That's something, considering the size of the group.
Weaknesses. Well, going by their outfits, they seem more like a citizen militia than a regular army. maybe discipline is lacking. Perhaps they don't work super well as a group. They also seem to have an unusual amount of patience with belligerence. Perhaps they think you'll come along peacefully, and will let their guard down, assuming all has been resolved. [hidden] You bet they are also rather susceptiblke to light magic, since pretty much everything else you've encountered in this dark world has been.
All in all, you think Freddie might be able to escape, maybe carrying one of you with him. But the rest of you are probably screwed if it comes to that.