Unlike prior seasons, Volume 6 has a single unifying story arc. The episodes all concern to varying degrees the very topical subject of Iran's ambitions to become a nuclear power, and the efforts of the United States Government to prevent this.
Of MI-5: Volume 4, my colleague Paul Marvis noted an "almost pathological need to slam the United States of America every five minutes," and I found much the same in my review of Volume 5. Well this rabid anti-Americanism has been tempered in Volume 6. Although the American officials on the show still act villainously from time to time and though there are still occasional jabs at American policy in the writing (especially regarding the use of torture), the vitriol has been dialed back considerably. Much more importantly for purposes of believability, there isn't the extreme number of pro-American neocons working within the British Government at cross-purposes with MI-5 as there were in Volume 5. This time the threats mostly come from abroad, and are only slightly more likely to originate with the Americans than they are with the Iranians.
The Iranian arc is generally well written with most episodes moving along briskly. Although several episodes contain at least one instance of the writers essentially asking the audience to buy in to a particularly unbelievable plot point, only one of the ten episodes is really a clunker in this regard.
As with nearly all spy shows of this kind, it often seems that the only agents anywhere solving anything are the handful the show focuses on. While this stretches the bounds of ordinary logic, MI-5 operates smoothly within the spy show conventions. When the principal characters of MI-5 do rely on outside help, it's typically limited strictly to supplying muscle in the form of SWAT teams to storm buildings; something that the generally gun-free MI-5 agents are ill-equipped to do themselves.
Unlike prior volumes, there's practically no sign, much less development, of the characters' private lives outside of work. We see none of single-dad Adam Carter's (Rupert Penry-Jones) home life, and what romance there is in this volume is kept within the family of spies: agent with agent, handler with asset, and agent with agent-to-be.
The ten-episode release of MI-5: Volume 6 is spread across five discs, though three discs would have done nicely. Unfortunately, the only conceivable reason for putting just two hour-long episodes on each disc is to attempt to justify the hefty $79.98 MSRP.
Optional English language subtitles are nicely sized, paced, and placed.
Since on American television each episode of MI-5 is cut by nearly ten minutes to accommodate commercials, no doubt fans of the show will want to view Volume 6 on DVD to see what they've been missing. Although this release probably looks as good as its British counterpart, viewers able to play Region 2 PAL-encoded DVDs can probably save money by importing the British release. Though the British releases of Spooks retail for £39.99, they're frequently on sale for a fraction of the cost of their US counterparts from Amazon UK.
Though the $79.98 MSRP is unreasonable for ten hour-long television episodes, MI-5: Volume 6 is recommended for fans able to find the release at a more reasonable price.