In 2014, in Costa Rica, Michael Light, an American runner, and his adventure racing team gets stuck on the first day after their leader takes the poor decision to kayak against the tide. Leo, one of the members of the team, is outraged that Michael has not paid attention to their opinions.After a 3 year lapse in his career, in 2018, Michael is not satisfied with himself and decides to race one more time with the hope of winning a race at last. He chooses two of his teammates: Olivia, a climber, whose father made a career in the same discipline; and Chik, an older racer, whose recovery from a knee injury is uncertain. However his sponsor imposes the 4th team member, Leo, Michael's original team member, and now a social media celebrity; and, much against his own will, Light accepts. They fly from the USA to the Dominican Republic for a 5-day race mostly through mountainous jungle terrain. On the second day of the race Michael gives meatballs to a stray dog at the transition camp. Much further ahead in the race, in the middle of the jungle, the dog finds them and does not stop following them. During their walk at night the dog saves Leo and the Team from falling off a cliff and they all adopt him as one of them and call him Arthur, the King. For the last part of the competition, and while they are leading the race, however, they have to leave Arthur on shore to kayak on sea. But as they see the dog is about to drown while following them, they go back and save him. The team is thus delayed and loses the race, arriving second. Arthur collapses on arrival and a veterinary finds he is severely infected by parasites, advising to put him to sleep to prevent further suffering, which Michael refuses. He manages to take him to the USA, where the dog is saved.The last scene, 18 months later, shows them running together on a ridge.