Mother's fate
The scene in front of him was clearly the entrance into the Watt's estate, the appearance was almost identical to how it was when he visited during the tea party. The main difference was the time of day, it seemed to be almost dusk, and the streetlights looked to have only just started turning on.
Arthur noticed movement down the street, a group of shadowy figures had started scaling the fence, and it seemed as though they had done so in a blindspot, as the security guard on duty failed to notice them.
Arthur, in his strangely ethereal form, began floating in the direction of the figures, his body passing effortlessly through the fence as he quickly closed the distance between him and the trespassers.