It was supposed to be a simple task: drop Cerberus off at the Gates of Tartarus, the prison doors for Equestria's greatest and most terrible monsters. Little did Twilight know it was host to an entirely different prison: the SCP Foundation.
Twilight is enthralled with the sheer amount of knowledge and power the Foundation contains. They are likewise willing to bring her on board. After all, who can stop a black ops facility that doesn't officially exist?
Celestia, if she has any say in the matter, and she promised there would be hell to pay if the Foundation harmed her student.