Synopsis: Since the destruction of the Obsidian Order, Cardassia is in trouble and has closed her borders. A fleet of Klingon ships arrives at DS9. Their commander, general Martok, tels Sisko that his fleet was sent by Gowron to help the Federation in her struggle with the Dominion. The Klingons cause trouble on the station and beat up the cardassian taylor Garak.
Later DS9 receives a distress call from captain Cassidy, whose freighter just left DS9, that she is being boarded by Klingons who claim to have an order from Gowron to search all ships for changelings, the founders of the Dominion. Sisko takes the Defiant and draws off the Klingons.
Meanwhile, lt.cmdr. Worf has arrived and Sisko briefs him. His tast will be to be a liaison between the Klingons and Starfleet, and to find out why the Klingon troops are on DS9. He discovers that the Klingons found out that the Cardassian Central Command has been overthrown and they suspect the Dominion behind this. Because Klingon and Cardassian space are close they have decided to invade Cardassia and whipe out the new government. Sisko informs them the Federation will not support this action. The Klingon warships cloack and leave DS9.
The Federation has openly disapproved the attack and Gowron has withdrawn the Klingon Empire from the Kithomer agreements. Worf is given the choice: support Gowron or remain in Starfleet. If the clooses the later, Gowron will dishonor Worfs family. He chooses not to support Gowron. Later Sisko contacts Gul Dukat, who is working for the civil government now, who tells them the situation is critical.
Worf wants te leave Starfleet, but Sisko refuses to accept this. He contacts Gul Dukat and offers the civil government asylum on DS9. Together with Worf he leaves with the Defiant to meet with a Cardassian ship carrying the government. When the arrive the ship is under Klingon attack. In the following battle they succeed in beaming the government on board and head back to DS9 with the Klingons in persuit. DS9 is preparing for battle. If Martok contacts DS9 and demands the civil government being transfered to him Sisko tells him that genetic screening proved that none of the members of the government were changelings, but nevertheless, the Klingons attack. Fortunately the station has had a massive upgrade on her defensive systems due to the Dominion threat so they can defend themselves. But when the Klingons partially destroy their shields the station is being boarded and man to man combats start. Just on time, Federation help arrives and the Klingons withdraw, not wanting a victory which would leave the Klingon Empire weak. Gowron however, states they will not forget this.
The Cardassian civil government returns to Cardassia Prime but the Klingons won’t withdraw from some Cardassian colonies. Worf wants to leave Starfleet and join the Nyberrite alliance but Sisko convinces him to stay.