3. Power Of The Daleks (1966)
Sadly, this adventure is missing from the BBC archives as it was erased in their boneheaded 60's and 70's policy of recording over old episodes to save videotape. It's of historical importance for many reasons, though, being not only the very first post-regeneration story but the first adventure for Patrick Troughton, too. In a wise decision by the showrunners, the concept of the Doctor's regeneration is sidelined by the spectacle of the return of the Daleks. The Daleks spend the majority of the story pretending to be servants of humanity, only gradually revealing their ultimate goals of extermination. This episode also features the first good look at the mutated, squid-like creatures inside the Dalek casings and also gives us insight into their method of reproduction - a Dalek with a large spatula picks them up and places them in their shells. No... seriously. Although the televised story no longer exists there is a fine novelisation available, as well as a special edition of the Doctor Who Magazine with surviving photos and a thorough plot summary. It's definitely worth checking out.