A large concentration of tetryon particles leads the Enterpise-D to an abandoned station and a gateway that may have been created by the solanagen-based life-forms previously encountered (TNG episode: "Schisms"). The USS Hornet joins the Enterprise to investigate. Captain Hagler's brother was one of the crewmen killed during the first encounter. A probe is discovered with two unknown ships fighting for its possession. Chasing them back to the station, the Hornet and one of the alien vessels are drawn into the gateway.