When Graham Williams became producer it was under orders of the BBC to tone down the series after the previous season caused great alarm especially with Mary Whitehouse of the National Viewers and Listeners Assosciation. A result of this is over the next 3 seasons humour is introduced into the show more and more.

The Doctor and Leela arrive on Fang Rock and find the lighthouse crew as slowly being killed off. After finding out the alien is a Rutan they amange to stop the mothership from invading Earth in Horror of Fang Rock.
The Swarm invade on Titan and K-9 is introduced and is taken on board after Professor Marius gives him as a thank you gift. The Fendhal attack in modern day Earth in the Image of the Fendhal then the Doctor and Leela arrive on Pluto in the future and face the collector in The Sun Makers and then they enter the Underworld. The season finishes with a trip to Gallifrey as the Doctor stops The Invasion of Time and Leela stays behind with Andred one of the Chancellory Guards and K-9.
Season 16 is the Key to Time Season where Romana is introduced and The Doctor's first adventure with her and K-9 mark II. The Doctor is sent by the White Guardian to find the first segment on Ribos where as disguised as piece of Jethrick, the most valueable space mineral for space travel, which is fought for between a poer mad prince and a petty thief in The Ribos Operation. The Pirate Planet is the next destination for the Doctor and Romana where the Doctor confronts the half robotic Captain.with plans to take earth as his precious latest collection of mumified planets. Romana and The Doctor end up in present day England and face a vicous cult in the search for the third segment of the key to Time in Stones of Blood. They find the fourth segment very quikcly in the fourth story, The Anriods of Tara, but end up dealing with anriod copies and a princess who looks simular to one of the TARDIS crew. The fifth segment is on the thrid moon of the planet Delta Magna where the mighty Kroll is the monster in the Power of Kroll. Finally the Doctor finally faces the Black Guardian, all against the backdrop of an interplanetery war of Atrios and Zeos.
Season 17 is arguably the series' most popular (mostly to a strike at rival ITV for the autumn of 1979 and it was a strike that would ultimately mean the series finsihes abrubtly early.) It starts off with Romana regenerating and the return of the Daleks, looking for Davros in the ruins of Skaro to help fight a war with the Movellans. Skagra is planning to destroy the world by going back to the start of creation by gaining enough money to build a time machine in City of Death (the story with the biggest viewing figures in the Classic Series' history and at the height of the ITV strike). The Doctor and Romana arrive on Chloris where they find a power hungry Lady Adrasta holding onto power of the scarce metal on the planet by chucking anyone she doesn't like into The Creature from the Pit. A ship called The Emress that can interface between different ships millons of miles away brings in The Nightmare of Eden. Finally Season 17 closes with the Horns of Nimon. This wasn;t supposed to be the last story that would be Shada but due to a strike it was never finished.
John Nathan Turner became producer of the series in Season 18 and with a new version of the theme, new starfield titles and a new cosutme for the Doctor, Season 18 brings Doctor Who into the eighties. Tom Baker decides to quit at the end of this season bringing about the longest serving Doctor's reign to an end.
The final Tom Baker season sees K-9 get a bit seasick in Brighton and then Romana and The Doctor ending up on Argolis trying to stop Pangol from trying to cause another war with the neighbouring Foamasi in The Leisure Hive. The planet Tigella sees the Doctor and Romana face Meglos. They then end up in E-Space and land on the planet Alzarius where the encounter that Marshmen and gain in a stowaway in the form of Adric in Full Circle. They come up against the Three who Rule and an old enemy of the Time Lords in State of Decay, finally they find the gateway to N-Space again but have to deal with a slave ship taking time-sensitive Tharils through to N-Space but their plan is thwarted and Romana and K-( stay behind to help the Tharils and Adric and the Doctor return to N-Space in Warrior's Gate. Adric and The Doctor then meet The Keeper of Traken and encounter a great Evil called Melkeur who turns out to be the Master and becomes part of the source that keeps the union of Traken peaceful. He eventually takes over the body of a consual, Tremas. The Doctor and Adric decide to do some repairs to the TARDIS and end up on Logopolis, but not before finding a stowaway in the form of Tegan Jovanka and Nyssa of Traken arriving to find her missing father. It leads to the Master inavertantly casuing entropy and the universe is falling apart. After making an uneasy alliance with the Master they end up at the Pharos Project, a copy of the one being used in Logopolis on Earth and it ends with the Doctor falling from the radio telescope nad regenrating with Nyssa, Adric and Tegan at his side.

Tom Baker is still seen over 30 years since he first took the role as the quintessential Doctor and quite rightly so but the series wasn't letting up yet, Peter Davison was to become the next incarnation of the famous Time Lord.