The Survival of the Daleks

"The Survival of the Daleks" is the second episode of the tenth season of Doctor Who, and the first half of a two part story arc involving the Dalek's return in Renaissance Venice. It is also the first time in the TARDIS for Christina.

Synopsis
"Leonardo da Vinci! One of the greatest genius of humanity! And the Daleks are using him to rebuild their race...." - The Doctor

On her first trip in the TARDIS, Christina and the Doctor arrive in Venice, 1500 AD, where Leonardo da Vinci is in his final years, but not is all as it seems. A band of Daleks are also in Venice, and one of mankind's smartest minds is the key to their survival.