How Udina's plotline works and is believable:
Udina has always been about advancing human interests--and his own political power--whenever the opportunity arises. He is ambitious, pragmatic, and possesses a certain cunning--yet he's also selfish and singleminded. Between the events of ME2 and ME3, Udina begins reaching out to pro-human terrorist organization Cerberus in some capacity or another. C-Sec Executor Pallin finds out, and Udina manipulates Bailey into eliminating him (see ME: Inquisition comics).
When the Reapers invade, Udina is violently thrown off of his laurels. Many of his fellow friends and coworkers died on Arcturus, leaving him the highest ranking Alliance politician alive (except for Hackett and Anderson). Torn between his desire to keep power as Councilor, his need to save the people of Earth, and his rage at the rest of the Council for refusing to help, Udina desperately turns to Cerberus for aid. They plan to--eventually--seize control of the Citadel and the Council, forcing the Council races and Citadel fleet to retake Earth and rescue humanity from the Reapers. Udina doesn't trust Cerberus but doesn't see any other options (building the Crucible is just another one of Shepard's foolish errands and will take too long to complete).
But the salarian Councilor is on his trail, thanks to Pallin's evidence, and Udina has to up the schedule of the plan. A large chunk of Cerberus forces hastily invades the Citadel, Kai Leng goes for the salarian Councilor, and Udina begins leading the rest of the Council (and his hand-chosen Spectre, Shepard's former squadmate) into Cerberus clutches. His plan fails, one way or another, and he dies with his dreams of retaking Earth crushed.
He may also have been indoctrinated--working closely with Cerberus--but this is just speculation.
Tl;dr: Udina's storyline isn't that unbelievable, it's just one of desperate measures and opportunistic power grabs.
Modifié par Warlock Adam, 12 juillet 2012 - 03:32 .