Natalie: Mr. Monk, what's going on?
Adrian Monk: Okay, I have a theory. It's completely crazy, but it would explain everything. Kyle and Dianne moved recently. At some point, Kyle must have found some of her old papers - personal papers - including the suicide note she wrote 25 years ago.
Captain Stottlemeyer: Her suicide note?
Adrian Monk: He realized that with that note, he could kill his wife with impunity. It was in her handwriting. Nobody would ever question it.
Dianne Brooks: [v.o.] "The depression is overwhelming. Give Tangerine a good home. No relief. Even today I was eating Rocco's with Adrian and Trudy. Breaking that glass in the quad today felt like the final straw."
Adrian Monk: But he had one problem. Because the note was 25 years old, obviously, there were a couple of things in it that were no longer true.
Natalie: Like the name of her dog.
Adrian Monk: Exactly. And breaking that glass. And eating at the restaurant "with Adrian and Trudy." That's what he was doing all weekend. He was recreating parts of her life to match that suicide note.
Natalie: So when we found out, we wouldn't be suspicious.
Lieutenant Disher: Why did he kill the nurse?
Captain Stottlemeyer: He had no choice. Katherine Rutherford read that note 25 years ago. It would have been made public. She would have recognized it.
Natalie: Oh, my God, Mr. Monk, he could be doing it right now.