Who is Hector MacQueen, Masterman from Murder on the Orient Express and what is their importance?

Hector MacQueen and Masterman present themselves as being in Ratchett's employ, which, indeed, they are. MacQueen is Ratchett's secretary, and Masterman is his valet. The truth, however, is that they were both formerly involved in the Armstrong household - MacQueen had strong feelings of affection and respect for Mrs. Armstrong, while Masterman was Col. Armstrong's man-servant.