A trailer for a documentary mystery story and thriller: Of all the defining moments of the last century, Guernica had the biggest impact. A totem of war’s devastating effects, it was a battleground for reporting and propaganda as Franco sought damage limitation for his reputation. Three paths crossed in this furore: the world’s most celebrated artist, the Generalissimo’s manipulative kingmaker and an American “embed” filming in colour. In the maelstrom of espionage and idealism swirling around ’30’s Spain, the web spun by conflicting accounts draws a trail southwards. As more war victims’ bodies are now exhumed in Malaga, the role of these connected “witnesses” faces an agonising reappraisal.