An unfamiliar Ceiling, the fall of Cadia

"You awaken to a room you don't recognize, your hands, they're not your own. Something's different, something's not right, you feel bigger, bulkier, and faster. You hear sirens going off, an alarm of sorts, fire, gas, maybe a call to arms? You're not sure you go outside and look up, the sky is NOT right, these swirling hues of blue, red, and purple, something deep in your gut tells you 'This is bad, this is evil' and this is where we start our journey"

Party wakes up as Space Marines and goes to fight against demons until the planet explodes.