Sonadow:The Shapeshifter

What if someone you knew was always mysterious and was hiding a secret from everyone else? Sonic met a person just like that. Shadow the Hedgehog. Sonic's known Shadow for a while now and Sonic starts to notice that something was off about Shadow. Then out of nowhere, they both disappear from the world. Sonic and Shadow have been gone for three years and everyone thinks them dead. Until Sonic's friends finds a clue about their existence. Will Sonic's friends be able to find their long lost friends or will they perish from the evils that were released by a strange force?