Story One: An Unearthly Child

While the first episode is an exception, this is a cave man story.  I think it's fair to say that with a story about time travel, cave men seem inevitable.  It's cliche, but I don't know if it was cliche in '63. Thankfully this is the only time in memory that the Doctor goes to cave man days.  It's not a horrible story, but certainly (first episode as exception) one of my least-favorite Hartnell-era stories.  It's the first historical Doctor Who as well.  Many of the first doctor's stories were historical (that is, they took place in a time of Earth's history)

You can find the synopsis in numerous places, and I'm not going to provide that here for many reasons.  If you haven't seen it, you shouldn't have everything spoiled for you, and if you have seen it, you already know.  If for some reason you did want a synopsis you can find them in numerous places online, including Tardis Data Core.  This said, there are and probably always will be spoilers in these posts.