In the episode ( Season 3, Episode 3 ), a mysterious blackout hits San Francisco, and Adrian Monk is called in to investigate whether it was an act of sabotage. Summary of the Episode

The episode features a cameo by Willie Nelson , whose concert is the target of the second blackout. "Monk" Mr. Monk and the Blackout (TV Episode 2004) - IMDb

The power goes out across half of San Francisco for a few minutes. While the power company suggests it was an accident, the police find a letter from a domestic terrorist named Winston Brenner, who supposedly died in a bomb blast years earlier.