4363. This series has had its ups and downs, but its been far more consistently good than the previous two. Now, that said, you don't need to know much about this series to watch "Space Enough and Time" (the episode I'm referring to), except that the Master is currently female and goes by "Missy", and the doctor is attempting redemption. That's about all you NEED to know.
Seriously, watch it if you can. Its... very VERY good.