Destrian had intended to slip his disguise off as soon as he saw Marlena and made sure she was on her own, so he was caught by surprise when he was attacked by someone he was certain was a demon. It took him a few seconds to gather his wits because he didn't have bad blood with any demon, and he knew better than to attack someone in their territory when he wasn't supposed to be here to begin with.
When he could finally think properly a few seconds later, he realized he couldn't retaliate because he was in a body similar to a particularly weak maid. It was by sheer good luck that his attacker didn't seem to want more than to back him up against the wall.
She had a vice grip on his neck and he could barely see her face but he didn't need to. He recognized the shape of her claws from the way they grazed his neck. They were exactly like Delaney's. This was Regina, wasn't she? He had heard about her from Marlena but he was yet to meet her.