For some 25 years, Ken Dornstein has been haunted by the bombing of Pan Am Flight 103 over Lockerbie, Scotland - a terrorist act that killed 270 people, including his older brother David. Only one person was ever convicted of the plot - who else was involved remains an open case. In this emotional and suspenseful documentary, Dornstein sets out to find the men responsible for one of the worst attacks on Americans before 9/11. From the ruins and chaos of post-Gaddafi Libya, Dornstein hunts for clues to the identities and whereabouts of the suspects, who he tracks for almost five years across the Middle East and Europe. He encounters new witnesses and unearths fresh evidence that brings him closer to the truth about what really happened. This is a rare, real-life spy thriller, but also a meditation on loss, love, revenge and the nature of obsession.