Arthur's eyes had followed Devon's when he said they weren't alone, as such he didn't see Aqua get grabbed until after she was in the air and there was nothing he could do.
Aqua, was shocked, and annoyed ... and pissed. she was in some hybrid's arms. he had snatched her out of the wheelchair and into the air.
she asked him where the beast had gone and she replied "how the f**k should i know?" she looked over her shoulders at him, a pitch black mist forming around them, her skin was slippery and as such she forced herself out of his arms and crouched on the roof in front of him, the black mist hopefully starting to obscure his vision, it did not obscure hers as it was her mist. "if you want to know just go to where the fight was, it's tracks are pretty frickin' obvious"

Arthur was pissed off. he didn't know what to do though, he saw Aqua force her way out of the thing's arms, but he couldn't do anything, the ground beneath him began to bend and wave but did not stumble him."Devon? do you know who he is?" he did, and it just made him feel more angry.