Bear Grylls welcomes 66 teams, who descend upon the island nation of Fiji in an attempt to conquer the World's Toughest Race: Eco Challenge Fiji.  On day one, racing teams face challenging ocean navigation and a steep mountain trek. Both elite and rookie teams race side by side as the intense tropical heat threatens to end one team’s race.

As the race continues through the first night, an athlete struggling with heat exhaustion manages to stay in the race. Lead teams paddle back to Viti Levu, as novice teams continue to struggle on the island trek. The bulk of the teams return to Viti Levu on Day 2, but a fierce tropical storm makes portions of the course too dangerous, forcing a critical decision to be made by Race Management.

The remaining teams prepare to resume racing, after the course was shutdown due to torrential rain. When weather breaks, the front teams look to build upon their lead, as they drive hard to Camp 2. Meanwhile, the bulk of the teams bike through ruggid terrain, as they head towards Camp 1. Fatigue, illness and poor decision-making slow the back teams down as the Day 3 cutoff looms.

All of the lead teams are equalized as they spend the night waiting for the river rafting to open, giving hope to teams chasing Team New Zealand. The teams further behind in the race build Bilibili rafts and float downstream. Team Out There fights to regain their spot among the leaders. One team faces a mechanical breakdown on the bikes that threatens to take them out of the competition.

As the lead teams approach the daunting Vuwa Falls rope climb, one team makes a bold move to try and distance themselves from the others, but will it pay off? Mid pack and slower teams endure extreme mud while mountain biking, while others navigate the white-water rapid section of the course. A biking accident threatens the future of one team’s race.

After suffering a potentially serious injury, one team must backtrack to seek medical attention for a fallen teammate. Lead teams suffer through the river pools above Vuwa Falls, but eventually reach the paddle board section of Leg 4. A veteran team falls from the leaders as one teammate is diagnosed with a severe case of hypothermia, putting their entire race in jeopardy.

A lead team falls farther behind as a fallen teammate faces a medical crisis. Lead teams press ever-closer to the finish line of the race, while trailing teams continue to suffer. Many racers think about their families as they seek motivation to continue. A lead team's race may come to a surprise end when they are forced to make a "mayday" call.

A team must be rescued from the open waters of the Pacific Ocean in the middle of the night. The first team arrives at the finish line and is crowned champion, followed closely by the 2nd and 3rd place teams. As many of the slower teams face the toughest part of the entire course, not all are able to continue racing and 2 teams are pulled off the course by helicopter rescue.

As the race progresses into the eighth day, more top teams reach the finish line. Slower teams, now face-to-face with the hardest section of the course, must find the motivation to endure the intense suffering required to finish the World’s Toughest Race.

The final days of the "World's Toughest Race" sees 29 teams still striving to make it to the finish line. Pushed to their limits both physically and emotionally, they must fight through their exhaustion and fatigue in order to beat the final cutoff at the finish line. Teams face either heart-breaking defeat or emotional triumph as Eco-Challenge Fiji concludes.