Possible Clues:

• Contents of scoop from China, perhaps — explosive stuff
• An explosive
• Explosive chemical mixture
• Explosive mixture (of tea?)
• Flintlock need
• Tea likely to go up?
• Shoot prisoner turning angry with a loud bang
• One of the shooting-party, the German, held prisoner making up explosive mixture
• Explosive article found in magazine
• Good - prisoner locked in below as this plot failed