While on a routine mission to recover secrets from the reclusive Nightsisters, Sidious is tricked by Mother Talzin into accepting a power even he may not be able to handle. When Darth Plagueis becomes infected with it as well, the Sith Order spins into disarray. But Sith do not give up easily, even if their Grand Plan may require some--recalibration.
Plagueis and Palpatine lose their tiny Sith Apprentice during a vacation to Yavin IV, and now must search for him.