“Broken Link” is episode twenty-six of season four of Star Trek: Deep Space Nine and the season finale.
Odo is suddenly struck with an illness and is barely able to maintain his form. Dr. Bashir examines him and, although he can to a degree see what is wrong, he doesn’t know how to treat it. There is only one group of people who can truly help Odo – the Founders. So, Sisko plans to take the Defiant into the Gamma Quadrant and ask for help. Garak wishes to accompany them in order to find out whether there were any Cardassians who survived the attack on the Founders’ original homeworld (they have moved) in “The Die is Cast”.
Once the Defiant enters the Gamma Quadrant, they are quickly met by Jem’Hadar ships along with one of the Founders after they start broadcasting for help. They were expected; Odo’s condition was caused by the Founders so that he could be brought back for judgement in the Great Link for being the first Changeling to harm another when he, a bit by accident, killed one in “The Adversary”.