Carl and Hamilton investigate an extraordinary collection of Celtic gold from the Iberian Peninsula that dates back thousands of years. Amongst the rare artefacts are a gold bowl worth over £1m, fine pieces of jewellery depicting the goddess Astarte, and a stone altar to the god Endovelicus which might have been used in rituals that involved blood sacrifice.

Travelling to Portugal, where most of the Celtic gold is from, Carl and Hamilton meet up with Joao, their long-time local guide and collaborator. The three men travel to the site of a very rare temple devoted to Endovelicus and explore how the temple might have been used to worship the god.

Carl and Hamilton meet up with forensic archaeologist and former police detective Roger Box. They want to find out more about the Roman symbolism that appears on the Celtic altar, and Roger takes them to the site of a Roman temple in the Cotswolds.