And having read a little way into it I can see why it ended up in a charity shop so quickly. It's a sequel to Visions of Sugar Plums, her Xmas story of a year or two ago, and only 164 pages. And like Visions of Sugar Plums it reads a lot like a Mary-Sue crossover fanfic, in which Our Heroine is the only way a super-powered super-hunk can think of to track down an evil super. The SP books have always had this Mary-Sue element, but it is usually a lot more subdued - here there is no obvious reason why SP should be the detective of choice when dealing with a rogue super, and attempts to justify it make it make the unlikeliness of the character a little too obvious.
I may be misjudging it, and as I said I haven't read much of it yet, but I'm not optimistic. More (possibly) when I finish it.