No, Jon Hamm and Daniel Radcliffe sharing a bathtub is not the start of some "Mad Men"/"Harry Potter" crossover fan fiction. The image and the teaser below are from the upcoming British miniseries "A Young Doctor's Notebook," a four-parter based on a short story collection by Russian author Mikhail Bulgakov set to premiere in the U.K. on Sky Arts on December 6th.
Radcliffe plays a young doctor working in a village around the start of the Russian Revolution, while Hamm plays the man's older self, with the two sometimes interacting. There's no U.S. TV premiere set up yet, but given the talent involved, it seems likely that someone will license it to air here soon.
Bulgakov's autobiographical writings on addiction and being a doctor also served as the basis of Aleksei Balabanov's excellent 2008 film "Morphine."