10 Doctor Who Episodes More Important Than You Realised
4. Underworld
As you work your way through the Doctor Who Season 15 box-set, it may be tempting to skip Underworld. It's long been derided as one of the low points in the Tom Baker era, due to its dreary story and over-reliance on green screen.
However, the fact that Underworld is the first Doctor Who story to use virtual sets is just one of two reasons that it's more important than fans give it credit for. Sure, the colour separation overlay (CSO) in Underworld is a perfect example of why innovations like The Volume are needed, but it stumbled so that Doctor Who in 2024 could fly.
Underworld is also a fairly big Time Lord mythology episode, exploring why they established the non-intervention policy that the Doctor so regularly flouts.
In the time after their war with the Great Vampires, the Time Lords involved themselves in the affairs of the wider galaxy. Opting to help the Minyans, they shared advanced technology that accidentally caused a nuclear war.
Horrified at the consequences of their actions, the Time Lords vowed to merely observe the universe, never involving themselves in the affairs of other species.
Until the Doctor came along, that is.