The Phi bomb is under construction in Russia and Katchoo is determined to stop it. Her diplomatic trip to Moscow is sabotaged by a dangerous KGB assassin and Zoe must complete the mission and find the man developing "the last bomb." Meanwhile, Stephanie retrieves one half of the Cleopatra scroll that started the new arms race and quickly discovers the author wants it back! The stakes have never been higher as Katchoo and friends try to leave Russia with one of the country's top physicists and bring a dangerous nuclear game to a stalemate!