Possible Clues:

• Be a bit mad, having lost the thread?
• Be slightly unbalanced and resolve a case -- how unorthodox
• It's not a handyman you need if there's an apple short of a picnic
• Be out to lunch and partake of a singular set of facilities in NW town
• Properly assembled furniture shouldn't appear unstable
• Employ on board son in Cornish town and be touched
• So become unhinged?
• Be slightly mad when it hasn't been tightened up properly
• A ship with a propeller certainly shouldn't be touched
• Behave oddly