McGuffin

Two squabbling strangers realize they share a common goal: finding evidence of what they think is a historically significant cosmic event that occurred at the Woodstock Music Festival in the 60s. One is consumed with recovering a guitar he lost there, and the other wants data to back up his doctoral thesis. They travel to Woodstock, meet a third person who has been haunted by that same event for years, and begin to search for evidence and an explanation of the phenomenon.
As they learn more about each other, they share their experiences at the festival and their personal dramas after it. Despite wide differences in temperament and experience, they pull together to understand the mysterious forces affecting them.
They make plans to search the area where the event occurred, but are frustrated by a phenomenon they refer to as 'being yo-yo'd.' That is, being thwarted by a subtle, but effective, time loop.
In time they learn the complex background story to the incident and discover a key, a literal key, to bypassing the time loop.