This is easily one of the best Asterix stories.
It begins with Getafix competing against his peers at the druids contest, and winning. Then we are introduced to the Goths, a warrior race bent on conquest but somewhat lacking in brains. Having spied on the druids contest, they kidnap Getafix for his magic potion.
Things don't turn out as planned for the Goths, as Asterix, Obelix and Getafix manipulate the different Gothic tribes to turn on each other. First, with the magic potion, and then without it. The Goths are too dense and busy fighting each other to notice the effects wearing off!
This leads to mayhem in Germania that lasts for years, keeping them out of Gaul. A brilliant story.