If someone told you today that there was strong evidence that the Central Intelligence Agency once turned a blind eye to accusations of drug dealing by operatives it worked with, it might ring some distant, skeptical bell. Did that really happen?

That really happened. As part of their insurgency against the Sandinista government in Nicaragua, some of the C.I.A.-backed contras made money through drug smuggling, transgressions noted in a little-noticed 1988 Senate subcommittee report.

Gary Webb, a journalist at The San Jose Mercury News, thought it was a far-fetched story to begin with, but in 1995 and 1996, he dug in and produced a deeply reported and deeply flawed three-part series called “Dark Alliance.”