The Twistrose Key, book 1Tone Almhjell2013

When a mysterious parcel arrives at her family’s new home, eleven-year-old Lin Rosenquist has a curious feeling she’s meant to discover what’s inside.

Much to Lin’s surprise, the ornate key contained in the parcel unlocks a spellbinding world called Sylver, hidden behind the cellar door. Sylver is an enchanting land of eternal winter, inhabited by animals that shared a special connection with children in the real world, either as beloved pets or tamed wild animals. In death, they are delivered to Sylver, where they take on a curiously human-like form and still watch over the children they cherish. While Lin is overjoyed to be reunited with her beloved pet, Rufus, she soon learns that the magic of the Petlings and Wilders is failing, and snow trolls want to claim Sylver for themselves. Lin must discover a way to stop them and save this enchanted world.