"Mandibles" is a dystopian novel set in the near future, where the United States is on the verge of economic collapse due to a massive debt crisis. The story centers around the Mandible family, who are wealthy but find themselves losing everything as the economy crumbles.

The patriarch of the family, Douglas Mandible, is a wealthy businessman who has always been obsessed with the idea of leaving a legacy. He is estranged from his daughter, Avery, who is a failed artist struggling to make ends meet. Douglas's second wife, Luella, is a former nurse who is the caretaker for his elderly mother, who suffers from dementia.

The story begins with Douglas's son, Carter, being released from prison. Carter is a former drug addict who has spent the last few years in jail. He reunites with his cousin, Florence, who is a former academic struggling to find work in the new economy. Together, they hatch a plan to rob a wealthy neighbor, hoping to make enough money to turn their lives around.

As the economy worsens, the Mandibles begin to lose their wealth and status. They are forced to sell their possessions, including their homes and cars, and move in together in a small apartment. Douglas's mother, who has been living in a nursing home, is sent back to live with the family. Luella, who has been taking care of her, begins to feel overwhelmed and resentful.

Meanwhile, Avery has joined a group of anarchists who are protesting the government's response to the economic crisis. She becomes involved with a charismatic leader named Esteban, who has a vision of a new society built on the principles of mutual aid and cooperation.

As the crisis deepens, the government introduces a new currency which is intended to replace the dollar. However, the government money is quickly devalued, as hyperinflation sets in. Food and other basic necessities become scarce, and the Mandibles are forced to rely on handouts and charity.

In the book's final act, the Mandibles decide to flee the United States and seek refuge in Canada. They make their way north, facing many challenges along the way. Eventually, they arrive at the border, only to find that Canada has closed its borders to American refugees.

The book ends on a bleak note, with the Mandibles stranded at the border, uncertain of what the future holds.