First, complete all the story elements of the game (deal with Marcia, beat on Narcissus, and do the staged fight with Commodus). Then on Day 48, Marcia will tell you that Commodus wants you to train with him. You must first refuse. She will ask you again. Accept this time. In the carriage, Marcia asks if you think it is time to liberate Rome. Select the "No" response. Kill Commodus when you fight him in his personal training ground. Narcissus is then framed for killing him. When Laetus comes to ask you on Day 49 to be Narcissus's executioner, refuse to do it. Decline both times when you are asked. Then on Day 50, do not leave you room and choose to "Sleep". You will then wake up on Day 51 and can continue to play. Note: The only way to "end" the game at this point is to go into Punishment mode, kill 100 guards, and escape.