This episode marks the first appearance of The Daleks creator, Davros in the modern Doctor Who series. He last appeared on television in the 1988 Sylvester McCoy serial Remembrance of the Daleks. The character also confronted the Eighth Doctor in the 2005 Big Finish Audio Adventure Terra Firma.

Davros, according to The Doctor, was slain in the first year of the Time War as he flew his command ship into the heart of "The Nightmare Child", but Dalek Caan, using his emergency temporal shift, was able to breach the Time-Lock surrounding the Time-War, and rescued Davros

The Doctor: Excuse me, what day is it?
Milk Man: Saturday
The Doctor: Saturday. Good, good I like Saturdays.

Jack: Gwen, Ianto. You okay?
Ianto Jones: No broken bones. Slight loss of dignity. No change there, then.

Rose: She can't hear me. Have you got a webcam?
Wilfred Mott: No, (Sylvia) wouldn't let me. She said they're naughty.

Harriet Jones: I thought it was about time we all met, given the current crisis. Torchwood, this is Sarah Jane Smith.
Jack: I've been following your work. Nice job with the Slitheen.
Sarah Jane Smith: Yeah, well, I've been staying away from you lot. Too many guns.
Jack: All the same, might I say, looking good, ma'am.
Sarah Jane Smith: Really? Ooh...
Harriet Jones: Not now, Captain.

Harriet Jones: Harriet Jones. Former Prime Minister.
Dalek: Yes, we know who you are.
Harriet Jones: Oh, but you know nothing about any human, and that will be your downfall.

The Doctor: You were destroyed, in the very first year of the Time War at the Gates of Elysium. I saw your command ship fly into the jaws of the Nightmare Child. I tried to save you.
Davros: But it took one stronger than you. Dalek Caan himself.
Dalek Caan: I flew into the wild and fire. I danced and died a thousand times.

Sarah Jane Smith recognizes the Daleks from the third Doctor adventure Death to the Daleks and witnessed Davros' death in Genesis of the Daleks.

The Doctor remembering the Daleks moving Earth before goes back to the 1st Doctor adventure Dalek Invasion of Earth, when the Daleks attempted to mine Earth's magnetic core and convert the entire planet into a movable weapons platform.

The Mr. Copper Foundation refers back to Mr. Copper, a humanoid alien who decided to stay on Earth after the events of Voyage of the Damned. Clearly he put his alien knowledge to good use.