The Codex by Douglas Preston

'Greetings from the dead', declares Maxwell Broadbent on the videotape he left behind after his mysterious disappearance. A notorious treasure hunter and tomb raider, Broadbent accumulated over half a billion dollars' worth of priceless art, gems, and artefacts before vanishing, along with his entire collection, from his mansion in New Mexico. At first, robbery is suspected, but the truth proves stranger: as a final challenge to his three sons, Broadbent has buried himself and his treasure somewhere in the world, hidden away like an ancient Egyptian pharaoh.