This Dark Endeavor — Kenneth Oppel

Victor and Konrad are the twin brothers Frankenstein. They are nearly inseparable. Growing up, their lives are filled with imaginary adventures...until the day their adventures turn all too real.

They stumble upon The Dark Library, and secret books of alchemy and ancient remedies are discovered. Father forbids that they ever enter the room again, but this only peaks Victor's curiosity more. When Konrad falls gravely ill, Victor is not be satisfied with the various doctors his parents have called in to help. He is drawn back to The Dark Library where he uncovers an ancient formula for the Elixir of Life. Elizabeth, Henry, and Victor immediately set out to find assistance in a man who was once known for his alchemical works to help create the formula.

Determination and the unthinkable outcome of losing his brother spur Victor on in the quest for the three ingredients that will save Konrads life. After scaling the highest trees in the Strumwald, diving into the deepest lake caves, and sacrificing one's own body part, the three fearless friends risk their lives to save another.