Possible Clues:

• Vital
• Absolutely necessary
• Critical sort of mood
• Monkey and queen with musical backing? It's a must
• Of vital importance, commanding
• Sort of mood not to be ignored
• Worker getting motorway taken up for nothing or something essential?
• 'What thin --s, cold affections' (Henry Vaughan, Silex Scintillans)
• Essential
• One maiden for every local leaving knight's command