The Three Musketeers and the Duke's Treasure

Set three/four years before the TV series, Athos and his two comrades, Aramis and Porthos, encounter a complication to their already hectic lives. Will this turn out to be helpful, or merely a hinderance, and can anyone work out what the Duke's Treasure is before it's too late? (I am SO bad at summaries it's seriously unfunny). Rated M for safety only, K would probably be fine.