The 10 best modern 'Doctor Who' episodes
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8. 'Human Nature'/'The Family of Blood'
Doctor: David Tennant
Companions: Martha Jones
Why we love it: During the long dry spell between the original series and the Davies reboot, Paul Cornell wrote a novel in which the Doctor becomes human for three months and becomes a teacher at a boys school in 1914. When the franchise returned to television, he adapted it for this two-parter that features arguably Tennant's best work of the series, first as the very human John Smith (who doesn't know he's really the Doctor, but shares enough resemblance for it to not feel like a brand-new character), who doesn't much want to sacrifice what he thinks is his own life to turn back into the Doctor, and then as the Tenth Doctor at the height of his cruel arrogance, administering amazingly harsh punishments to the monsters who attacked him and the school. The god who becomes briefly mortal is a familiar trope of fantasy and science-fiction; this two-parter is an outstanding example of why people keep returning to that well.