Imagine if you will, in between ME2 and 3, Shepard and Cerberus crew's ship is blown up, Shepard survives but is placed in cyrostatis and wakes up 50 YEARS IN THE FUTURE by Alliance Scientists.
Shepard: Who are you?
Alliance Scientist: We revived you. Now, you must work for us.
*without skipping a beat*
Shepard: Okay.
Cue the entire game full of cameos and character dialogue solely based around,"SHEPARD WHERE THE FUCK WERE YOU?! WE THOUGHT YOU WERE DEAD."
"I WAS IN CYROSTATIS."
/bioware writing