Shadow the Hedgehog, a failed wonder drug meant to cure Maria, struggles to find the meaning to his life. When the Earth National Defense raided the Space Colony ARK, they aimed to dispose of everything, including Maria and Shadow.

After Maria's tragic demise, Shadow is sent to a mysterious dimension known as White Space, in which he meets a mysterious one-eyed creature. The creature promises that Maria can be brought back to life as long as Shadow finds the Three Wishing Orbs.

(Source: Sonic Wiki Zone)