Mrs. Vandemeyer was sitting almost facing it, and Tuppence respected her mistress's lynxeyed powers of observation.
Mrs. Vandemeyer did not see Tuppence observing her.
mnli hypothesis: Mrs. Vandemeyer did not see Tuppence observing her. premise: Mrs. Vandemeyer was sitting almost facing it, and Tuppence respected her mistress's lynxeyed powers of observation.