02E09 - Aliens in a Spaceship

A reported find of 'two aliens' in a large vat proves the gruesome grave of human twin boys, Ryan and Matthew 'Matty' Kent, missing since years, burned at 300°. 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 -inside a car boot- 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...