Possible Clues:

• A Christie sleuth
• Belgian detective
• Detective raising cap outside city
• Agatha Christie's Belgian detective
• "To speak the broken English is an enormous asset" speaker
• Left out of main story involving old Irish detective
• Hercule -, detective (Agatha Christie)
• ... and her male one
• Recurring character who dies in the novel 'Curtain'
• Sleuth from Belgium