I smell silver
As Jareth approaches he says, "If ya attack me, no one will let ya free. I probably t'e only aside from yaself that thinks ya imprisonment be wrong an feel any need to do somethin about it."
He moves close enough to get a good look at the manacles and the waist cuff, without touching the being made of living fire. "Now move ya arm like so," he indicates to turn it, "yeah, no sigils."
He stands up and backs a few feet away from the Flame Lord, "Okay, no enchantments can see, fy friend be wizard who can shape metals, I can go bring t'em here, set ya free in a day or two. Can ya return to t'e City of Brass on ya own? Or do ya need help crossin t'e planes to get ya revenge?"
OOC: Of course this post is predicated on the FLame Lord not blowing a Self-Control roll, doing something stupid, and bungling the whole deal... if it does attack when Jareth gets "too close", I'll be happy to edit.
And of course teh chains not being enchanted against Shape Metal spells...