Premise: Mrs. Vandemeyer laid down the revolver on the edge of the washstand within reach of her hand, and, still eyeing Tuppence like a lynx in case the girl should attempt to move, she took a little stoppered bottle from its place on the marble and poured some of its contents into a glass which she filled up with water.
Hypothesis: Mrs. Vandemeyer threw the gun at Tuppence and asked her to drink water with her. 
Label: contradiction