Such Wicked Intent: The Apprenticeship of Victor Frankenstein, Book Two

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.