It is a stiletto.
You can tell it is a stiletto because when it is placed on the floor, the tall heel lifts up at the back and holds the foot at an angle. That is how stilettos work.
Here is the cover of Fifty Shades Of Grey imitator Bared to You by Sylvia Day. This is also a shoe.
It is a stilAAARGHo.
You can tell it is a stilAAARGHo because when it is placed on the floor, the heel shoots up so high, unless its wearer is walking up stairs, she'd be pushing her face along the floor screaming "AAARGH".
Here is a detail on the back of the book.
Look at the underside. Unlike the front pics, the shoe now has a sole. Which suggests to us that the shoe on the front cover is a bottomless pit which, we suspect, leads to hell. Probably.
We're with Melville House: we prefer the American cover.