The guys over at GameHounds have taken it upon themselves to point out what they feel are plot holes in BioWare's original Mass Effect. As the game's storyline is thoroughly examined, spoilers abound:
Saren seeks the Prothean Conduit, which is assumed to be a weapon but is actually a miniature Mass Relay that, in this case, allows travel from Ilos to the Citadel. Saren wants to use the Conduit to infiltrate the Citadel and start the process that turns the Citadel into a Mass Relay to let the Reapers into this universe and begin the purge again.
However, at the start of the game, Saren is a Spectre who answers only to the council and gets carte blanche wherever he travels. He is also resourceful and cunning, yet his best idea to activate the Citadel is to go on a quest that could be discovered. This seems very out of character, and while you could argue that Saren's partial indoctrination with Sovereign could have affected his judgment, that would only then serve to show that Reapers are idiots.
Consider the end of the game: Saren gets into the Citadel, makes it to the tower, meanwhile a Geth fleet, led by Sovereign, has begun an attack on the Citadel defense forces. Sovereign itself smashes through those defenses like a bear fighting gnats and makes it to the center of the Citadel to join with it when Saren hits the switch and closes the arms around it.
Considering that originally the Keepers did this, why did Saren need the Conduit?
He's a Spectre, he could have just gone to the tower after hours on (Spectre business) and activated it while Sovereign and the Geth came into Citadel space. No one would have been the wiser until it was too late.