Moralia, Volume XI: On the Malice of Herodotus. Causes of Natural Phenomena (Loeb Classical Library) Book

It's rare to see Plutarch mad, but he is in The Malice of Herodotus. He believes Herodotus tells malicious lies about most Greek cities, and undercuts heroic deeds by attributing base motives, usually with no evidence. He has a pretty easy time showing Herodotus loves to tell juicy, shocking stories, and often omits accounts of noble actions altogether, or impugns them.
Plutarch also points out the incoherence in some of Herodotus's calumnies. He frequently cites evidence lost to us, such as inscriptions and other writings.

It's pleasant to learn the Corinthians did not run away from Salamis, and the Thebans were not at Thermopylae against their will. I can't always tell who's right, as in the dispute over the timing of festivals and whether the Spartans almost made it to Marathon in time. But most of the time Plutarch makes a convincing case. When I first read Herodotus years ago, I could tell he was a know-it-all who loved to say commonly held notions were wrong. So it's satisfying to see the debunker debunked. His account is still fun to read, and the starting point for this period of history, but this essay by Plutarch pointing out his malicious lies should be read along with it.

The Causes of Natural Phenomena is full of weird notions, as one would expect. It's just one nutty thing after another. I was laughing to myself at his belief that rainwater is more nourishing if it comes with thunder and lightning; then I saw a footnote from the editor explaining why it is. So I had to laugh at myself instead-- score one for Plutarch.