Well, this hasn't happened to me in a while...

So having slogged my way through Tinker, Tailor, Soldier, Spy, I went and picked up The Spy Who Came in From the Cold. And I basically finished that novel on a flight from Hartford to Chicago, and didn't need a bloody flowchart to keep track of everything...

...but part of that was because about halfway through, I realized that an episode of Star Trek: Deep Space Nine had pretty much cribbed the entire plot.
The episode in question in from Season Seven and is called "Inter Arma Enim Silent Leges."  It was written by Ron Moore and is basically the most obvious preamble to what he'd do on Battlestar Galactica. 

Something at the end of the novel triggered my memory and made me go back to the beginning, where I found this gem from the spymaster Control:

"We do disagreeable things so that ordinary people here and elsewhere can sleep safely in their beds at night." 

And at the end, from the novel's protagonist:

"I'd have killed Mundt if I could, I hate his guts; but not now. It so happens that they need him. They need him so that the great moronic mass that you admire can sleep soundly in their beds at night. They need him for the safety of ordinary, crummy people like you and me."

And this is from the chessmaster in "Inter Arma..."

"The Federation needs men like you, doctor. Men of conscience, men of principle... men who can sleep at night. You're also the reason Section 31 exists. Someone has to protect men like you from a universe that doesn't share your sense of right and wrong." 

Yeah, Control's quote up above reminded me of the line from "Inter Arma..." so when I got to the trial, that was still kind of in the back of my head and I knew what to expect.

The last time something newer spoiled something older like this for me was when John Hurt had a cameo in Spaceballs, and that was considerably more direct.