Book #19 of the Papa Pontivy series.
The year is 1966. The Vietnam War is going strong and the tensions between China and the Soviet Union are extremely strained. With Red China declaring it had its own nuclear weapons. the fear in London is that China would likely bring about WWIII unless its small stockpile was eliminated. Papa Pontivy is asked to help out and he comes up with the idea of the Legion of the Thousand to pull it off.
Marshall has a tiny role and is hardly mentioned.