Down Styphon! is the eighth and concluding book in the Kalvan Saga begun by the late H. Beam Piper in 1964.

After years of war against Great King Kalvan, Styphon's House's control over the Five Great Kingdoms is in jeopardy. In Hos-Bletha there are two great kings and in Hos-Agrys the Prince-Regent's rule is threatened as the Prince reaches his majority. In Hos-Harphax the new Great Queen is taxing her subjects to the breaking point, while in Hos-Zygros Great King Phidestros openly despises Styphon's House. Only in Hos-Ktemnos is there a stable regime, that openly supports Styphon's House.

Nos-Hostigos is at peace for the first time since Kalvan landed on the Aryan-Transpacific, Styphon's House Subsector's time-line. Local threats in the Middle Kingdoms have been neutralized and Styphon's House is busy trying to regain their former strength in the Five Great Kingdoms. Some of the new Great Kings have no love for Styphon's House and its quest for power over the great kings. However, the Fireseed Temple's resources are huge, including large mercantile houses, tobacco and grain monopolies, along with the Great Banking houses. Great Queen Rylla decides that the time has come to reassert Hostigi power and return home to Hos-Hostigos. Not everyone is happy with this turn of events, but Rylla is a force of nature and asserts her will.

Now it's up to Great King Kalvan to find a way to make their return to the Princedom of Hostigos a permanent one. His first task will be to defeat and subdue the Zarthani Knights' great fortress at Tarr-Ceros. If he's successful there, next he will then have to beard Styphon's archpriests in the Holy City of Balph, the very heart of their power and influence.