The Six Degrees of Petrovitch. Michael is an AI of incalculable complexity trapped under the remains of Oshicora tower. Petrovitch will free him one day, he just has to trust Michael will still be sane by the time he does.

Samuil Petrovitch is a survivor. He survived the nuclear fallout in St. Petersburg and hid in the London Metrozone – the last city in England. He’s lived this long because he’s a man of rules and logic.

Theorem: Petrovitch has a lot of secrets. Proof: Secrets like how to make anti-gravity for one. For another, he's keeping a sentient computer program on a secret server farm - the same program that nearly destroyed the Metrozone a few months back.