Hi, I've read Peter's link and I'm still confused but have a bit more context. The sentence remains ambiguous. I agree with the forum's definition of "to have someone cold" and I disagree with everyone's interpretation of "beat", but I also don't have a clear explanation. These are just my definitions of the individual words-
Rookie - beginner, e.g. "rookie policeman"
to have someone cold - to have indisputable evidence of someone's guilt [usually] OR POSSIBLY BUT LESS LIKELY (which is what I initially assumed) to have ordered someone to be killed, with "cold" referring to the temperature of a dead body (? debatable in this context though)
racketeering - "racketeering" is a criminal activity in which a person or organization engages in a “racket.” A racket is when the criminal creates a problem for others, then offers to help them "solve" the problem, but only if they pay the criminal.
beat - This is correct, they did not mean "beef". That would make even less sense. A policeman's "beat" is the route which a policeman has to patrol. "Racketeering beat" COULD refer to a patrol that was specifically for the purpose of catching criminals engaged in racketeering. However, it may (less likely) refer to the fact that the "rookie" was on a racketeering beat, i.e. that he was on his "route" along which he would probably visit all the places which owed him protection money etc.
It COULD mean:
"I almost managed to catch your rookie red-handed as I was patrolling the streets, looking out for criminals engaged in racketeering activity."
"I almost managed to catch your rookie red-handed as he was on his racketeering route, extorting victims for money."
But it's really confusing without even more context. Why would Gordon have a rookie who was racketeering?