Pure Dead Frozen (aka Deep Fear)

As usual, the Strega-Borgia family can't seem to get a break:

They've just welcomed a newborn boy Strega-Borgia into the world, but before they can give him a name, he's snatched and replaced with a demon baby. Mrs. McLachlan, the super-efficient (and supernatural) nanny is back, safe and sound—but so is the demon Isagoth, and he hasn't forgotten what he wants from the Strega-Borgias. And evil Uncle Lucifer has resurfaced, but this time he has the added ammunition of a pact with S'tan the First Minister of the Headen Executive—otherwise known as His Imperial Inflammableness, his S'tainless Steeliness, and the Arch-Fiend. And S'tan himself is desperate to find the Chronostone, because. . . well, to put it bluntly, Hades is starting to freeze over, and without the Chronostone, he may never regain his power.

The family's got to be ready—because this will be the final battle between good and evil, the battle where winner takes all. And they're going to need all the help they can get. . . .