Aboard space station Deep Space Nine, Constable Odo suddenly collapses, and is taken to the Infirmary. Chief Medical Officer Dr. Bashir performs an exam, and determines that Odo can no longer maintain a solid form, but Bashir can't find an explanation as to what is happening to Odo. The only thing Bashir can do is to give Odo medical orders to remain under observation and to take a rest from his duties. Odo is reluctant to do so, but decides to obey the doctor's orders for the time being. Kira stops by, and brings him a report of the day's criminal activities. She hopes that this will take his mind off what is happening to him. While reading the report, he notices something that catches his eye. He then attempts to leave the Infirmary to investigate. He doesn't make it far, and loses his shape and collapses into a puddle on the floor.

Odo then comes to the realization that the only people that can help him are his own people, the Founders. With the help of Captain Sisko, Lt. Cdr. Worf, Dr. Bashir, Lt. Cdr. Dax, and Elim Garak, Odo is taken to the Gamma Quadrant aboard the starship Defiant. They are met by the Female Changeling and three Jem'Hadar soldiers. The Female Changeling tells Odo that the only way he can be helped is by coming with them to join with the Great Link. The Jem'Hadar soldiers then pilot the Defiant to the location of the Great Link, using a device to keep the location of the Great Link a secret. Later on in his quarters, the Female Changeling visits Odo, and by linking with him she is able to temporarily stabilize his condition. Odo quickly comes to the conclusion that he was somehow infected by the Changelings in order to force him into returning to the Great Link. He also learns he is to be judged by the Great Link, as he is the only changeling to have killed another of his kind.

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