Disclaimer: Syfy owns Alice, not me. But I'm fairly sure you knew that.
Hatter feels Alice clinging onto him as tight as is humanly possible. He already knew about her thing with heights, he can't imagine she'd be feeling any better flying. Hell, even he doesn't feel particularly secure up here, and he's the one who promised her they'd be safe.
Clenching his teeth, he quashes the uneasy feeling in his stomach that is brought on by the unbidden image of Alice falling from the flamingo behind him. He tells himself that if that happened, he'd be able to go into a dive and catch her, but he knows that's unlikely. He's having enough trouble just steering it straight, let alone performing any rescues at the same time.
He knows he'd try though. Above all else, he'd do anything to catch this Alice of Legend if she falls.
