10 Doctor Who Mysteries That Will NEVER Be Answered

The lack of a full series in 2016 meant that options for long-form storytelling were limited. There was, however, one thing connecting the two episodes that bookended this gap year: their antagonists.

There’s some debate as to what exactly this mysterious collective was called. In The Husbands of River Song, it was referred to as the Shoal of the Winter Harmony, while in The Return of Doctor Mysterio, it went by the much more concise Harmony Shoal.

And the questions don’t stop there.

At the end of Doctor Mysterio, a Shoal member is shown to have hijacked a UNIT soldier. Viewers could've been forgiven for thinking that this plot thread would be picked up in Series 10, but ultimately it was left dangling.

So what did happen next? Was this mole swiftly dealt with, or did it successfully manage to infiltrate UNIT? Is there a whole follow-up invasion that we never witnessed? Is it only a matter of time until Harmony Shoal gets its own Big Finish boxset?!

Either way, enough time has passed that a TV rematch is now almost definitely off the table.