How has tom been involved in this situation?

The farmer paid Tom a visit, and told Tom that he suspected that there was something dubious about the sale of Roxy. Tom had been confident, however, that that his mother's maternal instinct would prevent her from ever coming to St. Louis, as she would surely be aware of how much trouble this would get him into. Now that she has disappointed him with her arrival, Tom feels that he has no choice but to turn her over to the farmer, or else he will be forced to repay him (a proposition he cannot afford). Roxy is too clever for her son and figures he must have promised the master that he would assist in capturing her.