Mary Jackson prepared an assignment but John Becker was not ready to approve the result of the assignment which led to the disagreement between them.
It became evident later that John Becker had the wrong input data which made him the wrong party in the disagreement.
As in so many mystery novels, Roger Ackroyd is set in a small, isolated community where everybody knows everybody else. The isolated, close-knit setting 1) suggests that the criminal is someone who everybody knows, and 2) creates a paranoid, suspenseful mood, since the criminal is hiding a big secret from their neighbors. It’s also telling that the owners of the two most “important houses” in town are also the two main victims of the novel.
