This is the third Asterix adventure. It starts with Getafix getting ready to leave the village for the annual druid conference (which is what he was getting ready for in the previous book Asterix and the Golden Sickle, although both are still stand-alone). Unfortunately Getafix ends up getting kidnapped by the Goths who need a druid to help them invade the Roman-invaded France. It is down to Asterix and Obelix to rescue him.
A great story with the Goths talking in Gothic text, and lots of humour too what with all the running battles going on and such. The village feast scene returns at the end too. A classic Asterix tale.
(This book is listed on Amazon here.)