With any long running media property, you will come across stories where you can see what the creators were intending, respect the effort they put into executing said intentions, but find the item as a whole very lacking. This six episode series is one of those items with Who...and not just because it's six freakin' episodes.
The Tardis crew has found itself drawn to a peculiar planet. There are these weird noises that seem to actively affect the quartet--especially Vicki, who is visibly shaken. The Doctor and Ian go off exploring, leaving Barbara to keep an eye on Vicki. As the guys explore the landscape filled with strange structures and acid pools (goodbye, Ian's school tie...), they discover there is a strange force plucking at anything gold...which doesn't do Barbara any good, as that force drags her out of the Tardis by that bracelet Nero gave her in the last serial. By the time the Doctor gets back to the Tardis, he finds it--and Vicki--have disappeared.
To be honest, not a lot happens. You could pretty much make the argument that this half hour has a whiff of the first episode of 'Dalek Invasion of Earth' in its 'our heroes wander around until the monster shows up'....except the monsters are shown, but don't actually show up. While I liked some of the moments in this episode, it's hard not to see this as just wandering about waiting for the story to actually start happening. I particularly appreciated the conversation between Barbara and Vicki that takes up the middle portion of the story, where writer Bill Strutton actually starts trying to fill out the background of the new companion and sets up a tension between her and our favorite school teachers. Surprisingly, the conversation ends up creating a dynamic between Vicki and Barbara that is what we were promised with Susan but was rarely delivered on.
And then there are our monsters for this serial, the Zarbi, and the reason why this serial is admirable but doesn't quite work. The Zarbi are big ants. And since these are big ants made on the budget of a children's program in 1965, they're basically big plastic shells with the be-pants legs of the actors sticking out of the back so they can 'walk' around. Believe it or not, the production team had hoped that lightning would strike twice and these guys would be as popular as the Daleks, but it's just hard to take them seriously. The chirps that represent the Zarbis' 'language'--provided, apparently, by the avant garde group Le Structure Sonore--won't get on your nerves now...but just wait.
I think that this episode in and of itself is okay...primarily because most of it is taken up by Tardis crew character stuff. But keep in mind the key words here are 'in and of itself.'