Such Wicked Intent — Kenneth Oppel

Devotion turns deadly in this second Gothic thriller from Kenneth Oppel.

When does obsession become madness? Tragedy has forced sixteen-year-old Victor Frankenstein to swear off alchemy forever. He burns the Dark Library. He vows he will never dabble in the dark sciences again -- just as he vows he will no longer covet Elizabeth, his brother's betrothed.
If only these things were not so tempting.

When he and Elizabeth discover a portal into the spirit world, they cannot resist. Together with Victor's twin, Konrad, and their friend Henry, the four venture into a place of infinite possibilities where power and passion reign. But as they search for the knowledge to raise the dead, they unknowingly unlock a darkness from which they may never return.