Doctor Who: 10 Stories You Must Rewatch After The Power Of The Doctor

2. Survival

In the aforementioned scene in The Power of the Doctor involving the Master taunting Tegan, he also taunts Ace, with Ace launching back with another dig about last seeing the Master when he was half cat.

This jab is referring to the last-ever classic Doctor Who story Survival, in which Ace encounters the devious Master for the first time. Portrayed by Anthony Ainley, the Master is bringing humans to a sentient world where they slowly transform into human-cheetah hybrids. As a side effect of this, the Master has also started to transform into a cheetah, and needs the Doctor's help to escape the planet.

After being transported back to Earth along with Ace, the Doctor is then transported back to the cheetah planet by the Master, where they face each other in a final battle. At the last second, the Doctor rejects the violence and destruction on the planet and is transported back to Earth, leaving the Master to seemingly perish.

As always though, the Master finds a way to escape. No surprises there.