Which best explains the meaning of "set our doubts at rest" as used in paragraph 9? communicate a suspicion

begin an investigation

search for clues

confirm a theory

“By an inspection of the trains, and by reckoning the time. The local police had to be called in, they had to communicate with Scotland Yard, Hopkins had to go out, and he in turn had to send for me. All that makes a fair night’s work. Well, here we are at Chiselhurst Station, and we shall soon set our doubts at rest.”