In the hands of a mystery writer, divorce can serve as a source of conflict between characters and give credence to motives for crimes as diverse as fraud, kidnapping, and murder. Smart writers will give readers insight into the personalities and backgrounds of their characters if divorce is used as a criminal motive. And because divorce procedures can be drastically different from state to state and from one country to another, careful writers will explore the laws governing the setting of their story before putting pen to paper.
This latter point is very important considering the fact that, if a crime occurs, police can establish motive by examining the wording of a divorce decree. Animosity between a couple generally grows in proportion to the time it takes to complete the divorce process. Contested child custody matters and disagreement over division of property can prolong a divorce, increasing the financial burden on both parties and turning normally reasonable people into hated enemies. These same problems can turn a person against his/her lawyer, especially a lawyer who's given imprudent advice to his client.
As an example of how individual state divorce laws can affect a story, let's look at a hypothetical case set in the state of Illinois where I live. Let's say a woman with two underage children decides to divorce her husband. The lawyer she chooses urges her to apply for sole custody of her children, failing to tell her that, in Illinois, sole custody is seldom granted. He advises against shared custody, where children live for alternating periods of time with each parent, but fails to explain that shared custody is not the same as joint custody in Illinois. The lawyer gives this advice knowing that prolonged disagreement by the parents over custody of their children will inevitably increase his time on the case and thus his bill to the wife.
The husband hires his own lawyer, who explains that in 1985 the Illinois state legislature passed a law providing for joint custody of children in divorce proceedings. The statute adopted by the legislature requires a Joint Parenting Agreement that spells out "each parent's powers, rights, and responsibilities for their personal care of the child and for parity in major decisions such as education, health care, and religious training." The lawyer advises the husband to apply for joint custody since sole custody in Illinois would leave all those major decisions in the hands of his wife, effectively cutting him out of any determinations made regarding the welfare of his children. The husband agrees to the lawyer's suggestion. He also agrees to his wife being named primary physical residential parent in the Joint Parenting Agreement, which means his children will live with their mother while he retains visitation rights.
The wife's lawyer knows that if the husband counter-sues for joint custody, and the couple fails to produce a Joint Parenting Agreement, the court may enter its own Joint Parenting Agreement based on the couple's ability to cooperate with each other. The court could also order the couple to attend sessions with a court-appointed mediator who would then make recommendations to the judge regarding child custody. Extending the custody battle is in the best interest of the lawyer, not the parents. Once again, the lawyer can pad his bill for time spent counseling his client.
If I were writing this story as a murder mystery set in Illinois, I'd kill off the wife's lawyer, then have the police treat the divorcing couple as suspects. What would be their motive, you ask. Well, that's easy. The husband and wife have spent mucho dollars on lawyers' fees for an ill-advised custody battle. Both of them are now deeply in debt and regretting the fact that they didn't know Illinois law and didn't cooperate in signing a Joint Parenting Agreement. While aiming some of their anger at each other, the police can show they mainly blame the wife's lawyer for their troubles.
While custody battles happen all the time, the laws and procedures governing those battles can be drastically different given the place where they occur. An author who knows his state's or country's divorce laws can lend credibility to his story while building a suspenseful plot.