Secretly learn German?
I work at a small liberal arts college with a strong German heritage and connection, and I have several colleagues who speak German and travel to Germany often. This summer I'd like to secretly learn German and surprise them by conversing in German when we return to classes in the fall.
I'm picking up a German grammar book from the public library today and combing through the resources in the Wiki. Are there any other suggestions for learning the language under the radar?
ETA: My degrees are in music, so I'm familiar with pronunciation and a handful of words through performing German Lied in recital. So not quite starting from zero, but I definitely can't form a spontaneous sentence.