Kenneth Bulmer

First published in the U.S. by DAW Books in 1972. This U.K. edition published by Orbit (ISBN: 0860078027) is dated 1974. Cover art by Chris Achilleos. Alan Burt Akers was a pseudonym of Kenneth Bulmer.

First published in the U.S. by DAW Books in 1973. This U.K. edition published by Orbit (ISBN: 0860078159) is dated 1974. Cover art by Chris Achilleos. Alan Burt Akers was a pseudonym of Kenneth Bulmer.

Published by Panther (29) in 1952. Uncredited cover art by Gordon C. Davies.

Published by Panther (48) in 1953. Uncredited art by John Richards.

Published by Ace (D-369) in 1959 as part of an SF Double. Cover art is uncredited, though the Ace Image Library credits Ed Valigursky.

Published by Ace (F-104) in 1961 as part of an SF Double. Cover art by Ed Emshwiller.

First published in the U.S. in 1957 as an Ace Double together with "Star Ways" by Poul Anderson. This U.K. edition published by Digit Books (R505) is not dated but is circa 1961. Cover art by Brian Lewis.

First published in the U.S. in 1957 as an Ace Double together with "Star Ways" by Poul Anderson. First published in the U.K. by Digit in 1961, this 2nd edition (R672) is not dated but is circa 1963. Cover art by Henry.

Originally published in the U.S. as "The Earth Gods are Coming" as part of an Ace Double with Margaret St. Clair's "The Games of Neith" in 1960. This first U.K. edition from Digit Books (R539) is undated but is circa 1961, and includes an extra novelette "The Aztec Plan". Cover art is not credited.