Possible Clues:

• With 24-Across, well-known line of literature and film
• Holmes mantra, and a hint to this puzzle's theme
• ' - - , my dear Watson'
• ''Easy!''
• Word to Watson
• It's pretty basic, yet Marlene is confused
• Like some particles - and most things, to Holmes
• Real men, yet can be easily understood
• Primary
• Word to a fictional Dr.