The Orchid Thief A highly unlikely, but positively gorgeous crossover between Nero Wolfe and Doctor Who.
The author, Leviathan, does a superb job of capturing Archie Goodwin's narration and Wolfe's genius. The Third Doctor and the Tenth are both deliciously in character -- especially Ten's ADD. Martha is Martha -- brilliant and strong. She impresses Wolfe in a way that feels organic to his nature, and Archie in a way that's organic to his.
The plot was engaging and felt like it could have come from either of the source materials -- well, okay, certain elements put it more firmly in Doctor Who's wheelhouse.