Within one family, several members can each hold an independent, sufficient reason to want the same person dead, so the existence of a motive does not identify the killer. Solving the crime requires separating the many who wished for the death from the one who actually caused it.
An amateur detective, not a professional policeman, investigates a killing inside a Mexican family and finds that nearly every relative had grievances, debts, or resentments pointing toward the victim. By working through these overlapping tensions he isolates which of the many possible motives was the one acted upon.
Treating the household itself as the full field of suspects reframes a murder as an outcome of intimate relationships rather than of an outside intruder. The closest ties, inheritance, jealousy, and dependence become the most revealing evidence rather than background detail.