"Part I: Search by the Mule" was originally published in the January 1948 issue of Astounding Science Fiction under the title "Now You See It...".

"Part II: Search by the Foundation" was originally published in the November and December 1949 and January 1950 issues of Astounding under the title "...And Now You Don't".

The Mule, who had placed a hyper-relay on their ship in order to trace them through hyper-space, appears, and reveals that Channis is a Second Foundationer.

With only the two of them left, the Mule reveals that he has brought his ships to Tazenda and has already destroyed the planet, and yet senses that Channis's dismay is only pretense.

When the Mule experiences a moment of despair, the First Speaker is able to seize control of and change his mind; he will return to Kalgan and live out the rest of his short life as a peaceful despot.

He believes that the Mule's actions have made the Seldon Plan irrelevant and declares war upon the Foundation, intending to usurp their role in the formation of the Second Empire.

Kalgan eventually loses the war against the Foundation as the specter of the Seldon Plan adversely affects the performance of the Kalganians every bit as much as it bolsters the morale of the Foundationers.

He also reveals he has created a device capable of emitting mind static, which is harmful to individuals with mental abilities similar to that of the Mule and the Second Foundation.

Activating the device in the presence of the cabal reveals Anthor to be a Second Foundationer, and further interrogation leads to the discovery of the rest of his comrades who are subsequently detained indefinitely.

Unsatisfied with the ease by which the Second Foundation has been defeated and suspecting Arcadia's information to be planted through mental tampering, Dr Darell runs tests on his daughter to determine if she has been compromised.

Arcadia was unknowingly working for the Second Foundation, having been mentally adjusted shortly after her birth in order to prevent detection.

On its initial publication, Galaxy reviewer Groff Conklin described Second Foundation as "a thoroughly satisfying and adult play of the scientific imagination".

[3] P. Schuyler Miller reported Second Foundation to be "good, sound, middle-of-the-road science fiction with a carefully hidden surprise".

A complex of buildings on Trantor, the remnants of those saved from The Great Sack and those not demolished to provide metal for export, house a staff of technicians and analysts.