The one where the Cybermen show up in force...
It's the Season 5 finale! Don't expect anything too special though, judging on the previous five episodes. Doctor Who could do finales well, even in the 1960s (look at The Evil of the Daleks and The War Games for instance, and for a great example of a mid-season finale, look no further than Destruction of Time). However, The Wheel in Space brings Season 5 to a very disappointing end after a run of excellent serials through 1967-68.
The Doctor's ridiculous idea of sending two novice spacewalkers over to the Silver Carrier to get his Time Vector Generator takes a slightly darker turn when our hero openly admits that risking Jamie and Zoe's lives is worth it to save the lives of many. He's right, of course - maybe - but it's still surprising that it's his best friend he's willing to risk, and it gives this impiest of Doctors a darker tinge at the edges. However, this Doctor does not take the deaths of others lightly (as some Doctors do), and the moment he breaks the news of Gemma's demise to the others is a brief yet poignant counterpoint to his earlier pragmatism.