Possible Clues:

• Place for theatre musicians
• *Instrumentalists' place
• They play along with Detective Poirot for the ending in front of stage
• Place for musicians in theatre
• After jogging, their captors wind down in one
• Choir patters around in space for musicians
• Theatric pros playing here?
• Chorister apt to stray where band plays
• Conductor's station
• Theater area