idea from me.
Joker's Sister Hilary manages to Contact Joker on Normandy, and informs that Cerberus is hunting her down and try to kill her. Joker who is scared out of his mind about losing his sister, he calls Commander Shepard to the cockpit. Joker explains that he just gotten a call from his sister, saying that Cerberus is trying to kill her because of a secrets that she had stole from Cerberus, she was gonna turn over the secrets to Alliance soldiers, but it was postponed by an attack on the Alliance outpost. now the
Alliance Soldiers are protecting her, holding out for Normandy to Arrive with Commander Shepard.
Commander Shepard calls for mission briefing in the conference room. everyone comes here to conference room. Shepard explains that Joker's sister had contacted Joker, said she's in danger, needs an evac because she has secrets that she stole from Cerberus which are now trying to kill her.
Mission: Rescue Joker's Sister from Cerberus trying to kill her for stolen secrets that they don't want her reveal to Commander Shepard.
Spoilers Warning: the Secrets implicate Cerberus's leader, TIM, Council's Udina before Udina's death and TIM's death in ending.
Secrets shows that TIM, indeed knew Udina was a Reaper agent working for Reapers all along from events of ME1 leading up to ME3. he had made sure he kept eye on Udina, but failed to realize that he had too been a pawn in the ME3 ending. when Reaper Sovereign was destroyed, Udina first plotted to kill Shepard when Commander Shepard came back on Earth in ME3. he was gonna kill Shepard in Trial, but that second plot was stopped by Reaper Harbringer, he wanted Shepard Alive to face him later on. in this ending, Udina is stripped of his council ranks, and it comes to the point of Council's death, this is small cutscene where Udina says, "Damn you Shepard, Damn that woman who cost me my council status!" and now, you know the part.. he whips out a gun, he gets shot dead.
Cassandra: "amazing idea.. this should very well fit into the ME3 storyline. worth a try.."