Skulduggery Pleasant: HELP

After finding a nearly dead Valkyrie in her own home, stabbed by her reflection and her subconcious, Darquesse, Skulduggery and Valkyrie are on a quest to stop them both before they kill millions. The mortals are getting suspicious as more and more people are brutally murdered. Valduggery and Ghanith included!!! BTW Valkyrie is about 18 in this.