Four exceptional astronomers celebrate 50 years of work and friendship on a road trip in the southwestern United States, recapturing youthful adventures and recounting each other's influences on the most exciting period in astronomy's history. Filmed in California, Arizona, New Mexico and Utah in the USA, and Cambridge, England, the storytelling marries first-person narration, humor and beauty to produce a deeply moving portrait of life and friendship as the men visit telescopes, pause at the Grand Canyon, and re-take a hike that nearly defeated them when they were young. In old age and facing death, their journey through breathtaking landscapes and under spectacular star-filled skies provokes them to reflect on how their work on the universe has illuminated the individual, affecting their sense of religious faith, the purpose of life, and what is knowable and unknowable.