The maleficent seven / Derek Landy.

"From the world of Skulduggery Pleasant."

Tanith Low, now possessed by a remnant, recruits a gang of villains - many of whom will be familiar from previous Skulduggery adventures - in order to track down and steal the four God-Killer level weapons that could hurt Darquesse when she eventually emerges. Also on the trail of the weapons is a secret group of Sanctuary sorcerers, and doing his best to keep up and keep Tanith alive is one Mister Ghastly Bespoke. When the villains around her are lying and scheming and plotting, Tanith needs to stay two steps ahead of her teammates and her enemies. After all, she's got her own double-crosses to plan - and she's a villain herself.