Classicly

Her nose wrinkled in concentration. "Greer? Wasn't he the one who claimed to have discovered a sort of gaseous cloud in space? Our system was supposed to be approaching it; when it reached our atmosphere, it would prove a deadly poison to all life-forms on this planet."

"Yes—that's it. Well, it seems he was right. It's come—the green cloud. All I could see out that window was the nauseous swirls of it, and the people where they'd fallen in the streets. Neither of us can leave this building." He snapped on the tele-screen. It lit up; he could hear the faint hum of the machinery, but no images appeared. "Dead!"