Offering two stories for the price of one, the Shadow Planet and World Apart could be considered a singular representation of the mysterious planet tropes in Doctor Who. One follows the idea of a seemingly good world hiding a malevolent secret, while the latter embraces the fear of the unknown. Comparable to the shorter serials of the Classic era, each quickly cuts to the chase and trims down much of the usual fat which would drag out such a story; offering listeners just enough science fiction and time travelling nonsense, before moving on.
The actual core story itself largely serves as an exploration and examination of the characters over any core themes, largely focusing upon Hex and Ace. While there might be a major threat present in each one, and the Doctor is given a chance to show off his typical manipulative brilliance, this is ultimately where their strengths lie. For starters, with Shadow Planet we see the two forced to confront their most negative aspects a-la Star Trek's The Enemy Within, with the characters themselves almost directly commenting upon many of their greatest flaws and failings. While it plays towards the outcome you might expect, how each positive and negative trait plays off the other - and the immense talent of the cast in speaking to themselves for minutes at a time - borders upon openly riffing on typical Doctor Who tropes, giving it a surprisingly enjoyable meta quality.
Then, World Apart takes the idea of removing the Doctor entirely, trapping the companions on an utterly alien and very hostile world and seeing how they would react. This isn't simply some case of "The Doctor is gone, we are doomed!" but seeing how two characters well versed in surviving Daleks, Cybermen and the like could slowly come to terms with just how slim their chances of survival truly are, and how much they still rely on the Doctor in times of need.
Each is a fascinating bit of meta-commentary wrapped within a great story, but there is no denying each has its failings. Shadow Planet in particular unfortunately offers few to no curve-balls to keep the audience interested, and at many points the story seems oddly squashed in, as if it was planned to be a much longer serial. As such, the ending is an abrupt series of sudden plot twists, while several characters die but never last long enough to actually leave any impact when they're bumped off. Equally, World Apart has a fantastic set-up, but the resolution comes so quickly with so few answers, that anyone listening for the mystery itself might understandably feel cheated.
If you're a longtime Who fan, give them a look for the genre exploration and character commentaries, and for Big Finish's ability to create whole worlds from a few background sounds.
DOCTOR WHO – SHADOW PLANET & WORLD APART / AUTHOR: AK BENEDICT, SCOTT HANDCOCK / DIRECTOR: KEN BENTLEY / STARRING: SYLVESTER MCCOY, SOPHIE ALDRED, PHILIP OLIVR, BELINDA LANG, SARA THOM, NICKOLAS GRACE, AND BEN MANSFIELD / RELEASE DATE: OUT NOW