Several times on the bonus material for "Doctor Who and the Silurians", then-script editor Terrance Dicks explains the origins for that story's eponymous villain. With the Doctor exiled to Earth and the TARDIS disabled, Dicks was told by one of his writers that the show was now limited to just two story types: alien invasion, and mad scientist. Realizing he was painted into a corner, Dicks decided to invert the scenario by commissioning an alien invasion from a species that was already on Earth before man rose to prominence.
Thus was born the Silurians, the memorable (and mis-named) villains that recurred on "Doctor Who" enough times to fill out their own box set. The opening story, from 1970, is the longest and most intriguing: a team of scientists in the caves under Derbyshire inadvertently awaken a hibernating reptilian species that had been asleep for tens of millions of years. First in secret and then in the open, the Silurians attack not only the scientists but then all of mankind. From a low-key opening episode, the stakes escalate until the world is threatened by an Ebola-type virus in part six.
"Silurians" was Malcolm Hulke's first solo contribution to the series (he'd previously co-authored two Second Doctor episodes) and he became a mainstay of the Third Doctor's run on the show. DVD extra features are strong: the deepest audio commentary booth to date (seven show contributors rotate in and out) provides tons of insights; guest actor Geoffrey Palmer narrates a terrific documentary that compares the relatively gentle pace of the 1970 serial to today's more condensed and frenetic adventures. This choice of narrator is brilliant, to coin a phrase: not only did Palmer guest-star in a recent new "Who" episode, but his son also directed four episodes last season.
The second story, "The Sea Devils", is Hulke's sequel to the earlier story, featuring the inadvertent revival of a marine cousin to the Silurians. This is a far more action packed episode: the Doctor and the Master have a lengthy swordfight in episode two, and the cooperation of the Royal Navy leads to several land and sea combat sequences in the closing installments. There's a submarine subplot, and two comedy sequences that have since been duplicated in new "Who": the Master captivated by a children's television programme, and the Doctor and Jo staging a lengthy mime sequence through a plate-glass window.
The "Sea Devils" bonus features are highlighted by an unusual commentary booth: Dicks, producer Barry Letts, and show director Michael Briant exchange the usual compliments and potshots, but this time they're joined by Andrew Cartmel, the show-runner for "Doctor Who"'s final three seasons. Cartmel's run was characterized by tight internal continuity and very little navel-gazing into the series' past: to have him discuss a story nearly 20 years before his time gives fascinating insight into the type of "Who" he later chose to produce.
The final DVD, "Warriors of the Deep", comes from much later in series history (it opens the Fifth Doctor's final season in 1984) and has aged the least gracefully of the three stories. This time, there's no debate on whether or not the Silurians and Sea Devils can co-exist with the human upstarts, they're just out on a highly effective seek-and-destroy mission. There's hardly a smile to be had in 90 minutes, and the only survivor among the large guest cast does so impliedly and offscreen. Ingrid Pitt, the queen of horror flicks, has a thankless small role which doesn't allow her to exchange so much as a word of dialogue with the Doctor; her exit from the show was later derided by writer Johnny Byrne on an Internet newsgroup as "the mother of all drop-kicks".
The extras for "Warriors" are perhaps harsher than they need to be. Everyone involved in production -- director, writer, actors, visual effects designer -- shows up to get their kicks in. "Warriors" was one of my first stories as a young fan in 1984 and I'm sorry to see the story hasn't matched my memories; however, having everyone involved throw stones at it 25 years later is perhaps a bit much.
On the whole, though, the box-set features the entire Silurians/Sea Devils running story, with two classic Doctors and a boatload of moral dilemmas. Even if the best material comes at the beginning of the set, it's still a fascinating release.