"Improbable Cause" initiates a two-part adventure concerning the search for the Founders' homeworld, which concludes in "". Following first contact with the Founders, the Obsidian Order – a covert Cardassian intelligence force – ally themselves with the Tal Shiar, their Romulan counterpart, and launch a secret, pre-emptive strike to destroy the Founders' homeworld, hoping that the Founders and the rest of the Dominion will collapse. The Dominion successfully lures the fleets of the Tal Shiar and the Obsidian Order into a trap, eliminating both organizations. The plot establishes an atmosphere of suspicion amongst the Alpha Quadrant powers, initiated by the shapeshifters' abilities to assume other identities, which forms the basis of plots for Season Four.