Blake (Gareth Thomas) and his crew launch a search for a valuable crystal, necessary to decode messages from the Federation. At the same time, a space vessel that has been missing for 700 years returns to the Federation base. Unfortunately, the ship carries a deadly virus, which ultimately infects the all-important decoding crystals. Once again, it is up to crew member Avon (Paul Darrow) to figure a way out of the present predicament. "Killer" was originally broadcast on February 20, 1979. ~ Hal Erickson, Rovi