What Killed Frankie?

A fall down a manhole.

But in the cold open of the first episode, a street scene is seen. As a figure seen from the back walks toward a manhole in the middle of the street, the cover of the manhole slides horizontally off the manhole, and the figure turns and avoids falling into the manhole. Meanwhile Frankie walks toward the manhole and falls in, and finds herself in the underworld.

So who or what slide the manhole cover off the manhole, making it a deathtrap for the unwary Frankie?

No body and no thing was seen moving the manhole cover, making it seem like some sort of magic moved the manhole, possibly as part of some plot to kill someone. Possibly it was the intent to kill Frankie, or possibly someone one else was the target, and the intended victim was warned by Frankie's fall and avoided following her into the manhole.