Try trapping the orc in your place.

As you look out at the orc while pretending to be frightened and uncertain, you notice that it doesn't seem to have a keychain. It starts to pace around your cell, seemingly keeping an eye out for the intruder. Before long, it leans against the wall beside your cell, seemingly bored of patrolling. You likewise maintain the act of being trapped and helpless, fiddling quietly with the few objects in your cell. Picking at the bench, you find a nail starts to come loose.

This seems like a good enough chance to lure the orc in. You take the nail and start fiddling it in the keyhole not so quietly as you pretend to pick the lock. The orc takes notice and you shove the door open, hitting him with it, but not leaving yo room to get out. You back into the cell, dropping into the corner as the orc dives in to subdue you. You toss the keys across the floor, distracting and confusing the orc long enough for you to leap up, swing around, and grab the keys. By the time the creature can reverse it's direction you're already closing the cell door.

It rattles the bars, roaring. You don't know orc language, so you have no idea whether it's screaming insults at you or trying to alert the others of your shrewd turnabout. The other cells may or may not have something of interest, and more orcs may or may not be coming.