The Gamma Quadrant is home to a hostile empire known as the Dominion, ruled by the shape-shifting Changelings, whose will is enforced by their ruthless soldiers, the Jem'Hadar, and their administrators, the Vorta.
It features the return of several recurring characters and draws on plot lines from the third-season's "Improbable Cause" and "The Die is Cast", the body of the fourth season, and fifth-season opener "Apocalypse Rising".
At the Dominion internment camp where DS9 officers Worf and Dr. Bashir, the Cardassian former spy Garak, and the Klingon general Martok are being held, the inmates have built an illicit transmitter inside the prison walls.
Worf's refusal to surrender, defeating a series of Jem'Hadar opponents, inspires Garak to overcome his fears and continue working.
The Changeling Bashir's runabout is carrying a bomb intended to detonate inside the Bajoran sun, causing a supernova that will incinerate DS9, Bajor, and the combined Starfleet, Klingon, and Romulan forces.
The Defiant takes the risky maneuver of engaging warp drive within the planetary system in order to pull the runabout away from the star where it explodes safely.
In 2018, CBR rated "In Purgatory's Shadow" paired with "By Inferno's Light", as the 9th best multi episode story arc of all Star Trek.