Basically, everyone wakes up after a small explosion inside the TARDIS. They can’t remember what happened, and are increasingly paranoid. There is a lot of screaming again by Susan, a little too much, but there is also a lot of tension between the characters. They try to attack each other, drug each other and accuse each other of sabotage.

SPOILER: This is the first episode that the TARDIS is hinted to be sentient. There is a switch that is broken and the TARDIS took them to the beginning of time. All of the problems on board were the TARDIS trying to warn them of what was happening.

This was the cheapest Doctor Who serial ever produced. It was written to be filler for the 13 episodes ordered, and it only used preexisting sets and the main cast. They call it a “bottle show” because of that.