Mathematician Harland Emple, an Irregular, hires Sherlock and Joan to find his missing grad student Lily. Harland fears he will be a suspect if anything has happened to her. Two FBI agents come looking for Harland and say Lily's been kidnapped, with a half-million-dollar ransom. They suspect Harland. A man who was leasing a minivan as a room at the kidnap site saw Lily being grabbed. Jimmy Cantrell, an ex-con, is found dead where the kidnap car was abandoned. Sherlock thinks Lily was kidnapped to do math for the kidnappers. The ransom demand was made by Cantrell after he found out she came from a wealthy family, and his partner killed him for that. Marcus finds Cantrell's bookie, Sylvia Kosar. Sherlock accuses her of rigging her Bingo games. Sylvia said Cantrell paid off his debts to her. Joan confronts Sherlock about his lack of relationships. Harland calls to say Lily has shown up unharmed. Lily said her kidnappers wore masks. Lily said she escaped from a car trunk because she was afraid she was going to be killed. Lily was being made to help redesign a FEMA flood map that Harland had developed. They suspect Adam Braun, an insurance agent who would benefit from the new map by selling flood insurance. Harland told Lily how he felt about her. Sherlock suggested looking at areas which would benefit from the revamped map. Joan recognizes a name from a list of those who benefitted. That was Marvin Hathaway, Cantrell's landlord, who has land in that area that was being considered by a tech company. He was in the regional FEMA office the same day that Lily was. A spot of Lily's energy drink had been found in one of his properties. Sherlock invites Athena out to dinner, and she accepts.