The Stone of Darkness, Book 3 in the Dragonslayer Series
A murderer is closing in on Sophie. Using a secret, prototype machine, she makes exact copies of herself, believing at least one of them can escape. She does this knowing the process destroys the original, meaning her.
The Sophies come to life not knowing what has happened, because the process also destroyed their short-term memory. They separate, each one desperate to piece together the missing facts from the last few weeks of Sophie’s life before all of them are hunted down and killed.