Episode 9 of The Trigan Empire
The Phials of Forgetfulness
aka Vannu’s Poison
The Lokan Invasion (The Collection)
Stad zonder geheugen (Dutch title)
City without Memory (Dutch title, translated)
Written by Mike Butterworth
Illustrated by Don Lawrence
The Phials of Forgetfulness was originally published in 6 instalments in issues 274 (15 April 1967) to 279 (20 May 1967) of Look and Learn magazine.
It was reprinted in 1975 in Vulcan comic.
It is reprinted in Volume 2 of The Trigan Empire—The Collection (the Don Lawrence Collection).
It is reprinted in Volume 1 of The Rise and Fall of the Trigan Empire (Rebellion).

Plot summary
Janno and Keren go on a reconnaissance flight to Fort Rabelli. The entire garrison has disappeared. Suddenly, Keren attacks Janno. Janno overpowers him and brings him back to Trigan City.
The fort had been occupied by Lokans under the command of Vannu. Vannu possesses a liquid that causes memory loss. The entire garrison had drunk it. Since Peric doesn’t believe the story and claims Keren simply had a sunstroke, Janno insults him. Trigo wants to imprison him for that, but Janno escapes.
Vannu poisons all the drinking water in Trigan City, causing everyone to stare blankly into space. This allows Vannu to seize power. Only Janno remains clear-headed and discovers there is an antidote.
Trigo’s blood brother, Imbala, the king of Daveli, comes to Trigo’s aid. They set up camp near a water spring close to Trigan City. Vannu wants to poison this spring as well and sends someone to do it. Janno foils the plan. When the Lokans attack, the Davelians are not addled and they are victorious.
Links
Plot summary (Dutch)
275
https://www.catawiki.com/nl/l/3336531
Downloads
MediaFire via British Comics Compilations