Modal is set in an America in which global warming is raising the sea level and driving desperate coastal populations inland. The combination of population displacement and fierce and frequent storms has wrecked technology and devastated towns and cities. Social unrest has spawned multiple private armies that prey on the surviving productive element.
Modal contains scenes of violent action, mingled with the emotional problems of complex personal relationships. Its protaginist, martial arts expert Jaghon Nobile, becomes involved with two very different young women: Cailleaghn, who is cultured for her time, and Lordage, who is a tough female trooper. When Prince Godar, the local ward baron and boss of the town's private army, rapes Cailleaghn, Jahgon flees with the women and others, ultimately taking a Huck Finn-like trip down the swollen Mississippi River on rafts in the hope of forming a new and saner society.
Throughout the story, Jaghon is trained in modality, the use of multiple intelligences, by Werster, an elderly psychologist. The climax is a classic duel to the death without weapons.