The disappearance of Jane Finn was forgotten and the whole affair was lost in oblivion." Mr. Carter paused, and Tuppence broke in impatiently: "But why has it all cropped up again? 
Jane Finn cropped up again because someone was doing research.  
mnli hypothesis: Jane Finn cropped up again because someone was doing research.   premise: The disappearance of Jane Finn was forgotten and the whole affair was lost in oblivion." Mr. Carter paused, and Tuppence broke in impatiently: "But why has it all cropped up again? 