Here are some choice lines:
Justin Playfair (Scott) is a millionaire who retreats into fantasy after the death of his wife, imagining himself to be Sherlock Holmes, the legendary fictional detective. Complete with a deerstalker hat, smoking pipe and violin, he spends his days in a self-constructed criminal laboratory, constantly paranoid of plots hatched by his (that is, Holmes's) arch-enemy, Professor Moriarty.
When his brother (Lester Rawlins) places Justin under observation in a mental institution, and conspires with his former business associate to get his power of attorney, Justin attracts the attention of Dr. Mildred Watson (Woodward), a psychiatrist who becomes fascinated by his case. After Justin demonstrates a knack for Holmesian deduction, the institution releases him, and Watson meets with him at his home. Playfair is initially dismissive of Watson's attempts at psychoanalyzing him, but when he hears her name, he enthusiastically incorporates her into his life as Dr. Watson to his Holmes.
The duo then begin an enigmatic quest for Moriarty, with Playfair/Holmes following all manner of bizarre and (to Watson) unintelligible clues, growing closer to each other in the process.
On a personal note, I still can't watch this film without crying like a baby. You've been warned.
Justin Playfair: Dear friends, would those of you who know what this is all about please raise your hands? I think if God is dead he laughed himself to death. Because, you see, we live in Eden. Genesis has got it all wrong. We never left the Garden. Look about you. This is paradise. It's hard to find, I, I'll grant you, but it is here. Under our feet, beneath the surface, all around us is everything we want. The earth is shining under the soot. We are all fools. Ha ha. Moriarty has made fools of all of us. But together, you and I, tonight... we'll bring him down.
Justin Playfair: Just keep saying to yourself "I'm adequate."
Dr. Mildred Watson: You're just like Don Quixote. You think that everything is always something else.
Justin Playfair: Well, he had a point. 'Course he carried it a bit too far. He thought that every windmill was a giant. That's insane. But, thinking that they might be, well... All the best minds used to think the world was flat. But what if it isn't? It might be round. And bread mold might be medicine. If we never looked at things and thought of what might be, why we'd all still be out there in the tall grass with the apes.