The planet AR-558 is notable only for being the site of a major Dominion communications relay. It has already been seized by Starfleet soldiers, and paid for in blood; of the 150 sent to the planet, 43 still live, and they have not been rotated off-duty for over five months. This is in contradiction of Starfleet regulations, which insist that infantry be rested every 90 days.
The USS Defiant arrives carrying supplies and replicator rations. Captain Benjamin Sisko commands, with Worf as executive officer, Ezri Dax and Dr. Julian Bashir along as tech and medical support, Ensign Nog as a crewmember, and Quark, sent on a "fact-finding mission" by the Grand Nagus.
After an abortive error involving friendly fire, Sisko lands on the planet and begins to assess the situation. The Jem'Hadar are very interested in regaining their communications relay; Lt. Nadia Larkin, ranking officer, is just as insistent that Starfleet keep it, but with the Dominion supplying fresh troops and Starfleet doing no such thing, the odds don't look good. Furthermore, Bashir's professional medical opinion is that the soldiers are in bad need of being replaced, a fact simply not logistically possible. Ezri becomes an ad hoc assistant to the garrison's engineer, Kellin, in helping him decode and decipher the comm relay. Nog looks up to the battle-hardened veterans as heroes, to Quark's consternation; the elder Ferengi has seen the brutal, nastier side of these "hew-mans," and he warns Nog not to become too enamored of them. Finally, Sisko is pushed into a decision when the Defiant comes under attack. He orders Worf to take the ship to safety; he and his men are staying to fight.
Sisko begins by fortifying the garrison's defenses. The Dominion have left a set of booby-traps: "Houdini" anti-personnel mines that can pass in and out of subspace at random. Kellin and Dax work out a way to force them into normal space, so that they can be moved out of the camp and used to stop attacking Jem'Hadar. He also sends out a scouting party to locate the Jem'Hadar base; Lt. Larkin leads, with Reese as survival expert and Nog as talent: his Ferengi ears will work where jammed tricorders will not. Quark naturally objects. The party gains the needed intelligence but is ambushed; Larkin is killed, and Nog loses his leg.
The remaining Starfleet personnel prepare for the upcoming fight. Quark guards Nog in sickbay. Bashir sets up an audio broadcast of holosuite singer Vic Fontaine as Houdinis begin exploding. Vargas and Kellin die. Quark kills a solder threatening Nog.
Most of the Federation personnel are dead but the station is held and the relay is tapped. New supplies of troops arrive via the USS Vera Cruz, as well as a dedicated tech crew to commandeer the relay station; the Vera Cruz is also evacuating the wounded, including Nog, who will be fitted with a prosthetic limb. Nog's recovery is detailed in the episode "It's Only a Paper Moon". With control of the comm relay, Starfleet will be able to tap into Dominion communications throughout the entire sector.