Sapphire and Steel may have been assigned, but Zero starts with Silver showing up to help a disgruntled Gold, who feels competent to handle the latest breakout on a shuttle orbiting Earth. Silver’s appearance only convinces Gold that management still doesn’t take him seriously, and his resentment is about to grow because Silver takes one look at the situation – astronaut bodies everywhere, each dead of a different cause, and something pounding on the outside of the airlock as if it’s knocking to get in – and calls for even more help.

The murders, the monster in space, the voice on the radio only able to respond using words that have been spoken by others – Zero is suffused with the creepiness requisite for a good Sapphire & Steel story. The tone throughout is a ghostly combination of Stephen King and Edgar Allan Poe in space.

But my favourite parts are the casual discussions between the operatives. Like any co-workers who don’t see each other often, a shared mission rapidly becomes a chance to talk shop. These conversations not only illuminate each operative’s character, but give the best glimpses yet into their lives. Gold resents the human race for being the source of so many breakouts. Silver and Sapphire are downright chatty – they compare notes on times each other has been trapped, she has messages to pass on from Mercury, and he wants to gossip about his former mentor Copper. Even Steel is willing to talk about the challenges he has faced and how far he is willing to go to accomplish his mission. Although the words “bomb squad” are never spoken, even more than TV episodes or audios where the operatives get trapped, Zero illustrates just how dangerous and difficult their job is. Dangerous… and also seductive. Because what Silver really wants to talk about is the rumours he’s been hearing, the ones that Copper hasn’t been trapped somewhere, but that he has instead switched sides.

Unfortunately, Zero is not a true standalone story; Gold spends a lot of time hashing over the second-season audio The Perfect Day, and much of his character was outlined in premiere audio The Passenger, both penned by Lyons. Fortunately, all three are worthy listens and even make a good standalone trilogy for anyone just starting out in this Big Finish audio range.

Zero (by Steve Lyons; starring David Warner, Susannah Harker) was released by Big Finish Productions in June 2008.