I want to know their personalities, their relationships, the nature of the party itself. I want to drabble in a 'Guns of the Soviet Union' esque scenario, so this would be a massive help.
The Russian Revolution by Sheila Fitzpatrick is very good. If you're looking for more detail on long-term party relationships and the Union as a whole, the Soviet Experiment by Ronald Suny is great but expensive as all hell from what I can see.