Nine short stories from a few of the greatest names in science fiction on the topic of exchange, replacement, upgrade, and masquerade. Ranging from true short story length through novelette and originally published in science fiction magazines in the 1950s, these brief escapes into improbable worlds have it all: humor, suspense, betrayal, mystery, twists, and of course-robots and aliens. THE BIG TRIP UP YONDER by Kurt Vonnegut, Jr. THE JUDAS VALLEY by Randall Garrett and Robert Silverberg THE MOON IS GREEN by Fritz Leiber OLD RAMBLING HOUSE by Frank Herbert PIPER IN THE WOODS by Philip K. Dick SENTIMENT, INC. by Poul Anderson THE TUNNEL UNDER THE WORLD by Frederik Pohl YEAR OF THE BIG THAW by Marion Zimmer Bradley YOUTH by Isaac Asimov