Plot Hole: Several plot threads are left dangling at the end, notably the destiny of the Kraal fleet led by Chedaki (described earlier as powerful enough to conquer Earth without the androids and virus) and the fate of Sarah's android.
Plot Hole: It defies belief that Crayford, for two years, would never have looked under his eyepatch, never have realized his eye still worked, never even tried to clean the supposed injury site.
Revealing Mistake: When the Doctor enters the real Defence Centre, the sliding doors don't close all the way.
Factual Error: When Crayford's ship returns, the jettisoned android pods are mistaken for "meteorites" by the Space Defence Centre staff. Technically, they would be called meteoroids.
We learn that Benton has a younger sister.
Surely the space centre would have wondered why Crayford was wearing an eyepatch when he appeared on the visual monitor, since he left Earth without one?
The Doctor: Nobody knows who's who.
Harry: Sarah, old thing, what's going on?
Sarah Jane: Well, for starters, you've got a very nasty twin!
Sarah: So, providing we don't burn up on re-entry and aren't suffocated on the way down, we'll probably be smashed to a pulp when we land.
The Doctor: Exactly. Sarah, you've put your finger on the one tiny flaw in our plan.
Sarah: Our plan? It's your plan!
Sarah: Must have blacked out.
The Doctor: Yes, you did. The G-force cut the blood supply to what you humans laughingly call your higher centres.
Sarah: I hate sarcasm, especially when I'm dying.
Final appearances of Ian Marter as Harry Sullivan and John Levene as RSM Benton.
It had been planned to feature Nicholas Courtney as the Brigadier, but other commitments prevented his appearance.