The death of Pedro Calderón de la Barca – soldier, priest and one of the finest dramatists Spain has produced – continues to prove almost as turbulent and unpredictable as his long and improbable life.

Four centuries after Calderón died in Madrid aged 81, researchers believe they could be close to finding his remains, thanks to the deathbed testament of a priest, a key long guarded by the playwright’s family and the latest in ground-penetrating radar.

Calderón, whose most famous play, La vida es sueño (Life is a Dream) is a violent examination of fate, free will and the nature of reality, died in 1681 and was buried by his priestly brotherhood, the Congregation of St Peter the Apostle, in a church in the centre of Madrid.