2014, Turkey. A surveillance flight over Lake Iznik reveals the sunken remains of a 4th-century Byzantine basilica. This church is located on the site of the ancient Roman city of Nicaea. This city is said to have hosted one of the founding moments of Christianity, ordered by Emperor Constantine: the 1st Council of Nicaea. From Turkey to the Vatican, from Oxford to France, an international scientific team will conduct a double investigation, historical and scientific, to unravel the mysteries surrounding the sunken basilica of Iznik.