A reported find of 'two aliens' in a large vat proves the gruesome grave of Ryan and Matthew 'Matty' Kent, twin teenage boys who have been missing for years. It's again the work of "the Gravedigger", a serial kidnapper-murderer who buries his victims and demands a royal ransom, no negotiation. The twins had not enough air to survive even if the ransom had been delivered as demanded, but after examining Matthew's serious fracture and stun gun wounds, the team concludes it was a car crash, the Gravedigger was surprised by the second twin and has no larger vat available. Now the Gravedigger kidnaps both Bones and Hodgins from the Jeffersonian parking-lot, asking $8,000,000, well within his family's means. Zach discovers why the vat contains so much blood: Ryan severed his own artery with a pen, to give his brother more air and hence time. The forensic hostages - buried alive in a car - aren't found within the ultimatum, but use enough tricks to gain time by saving and making oxygen, send a numeric message which makes relevant geological sense to erudite genius Zach and attempt an outbreak with a (last?) bang.
—KGF Vissers