12 Abandoned Doctor Who Subplots

We first encounter the head-splitting species as The Shoal of the Winter Harmony in the The Husbands of River Song. By the following Christmas special (The Return of Doctor Mysterio) they've rebranded themselves as "Harmony Shoal" - complete with a twirling Daily Planet-style globe atop a swanky skyscraper, and a very insidiously appropriate "open your minds" tagline.

Eventually, like with every superhero tale as old as time, the Doctor and Superman-lite save the day. Moments afterwards, Mr Brock warns the Doctor:

"The vengeance of Harmony Shoal is known and feared throughout the five star systems!"

This is swatted away with typical Doctor panache. However, whilst UNIT descend on Harmony Shoal's New York HQ, we see one of these multi-nucleate organism, functioning as an infinitely adaptable, independently functioning, peripatetic central nervous system creatures subsume a UNIT soldier. Surely enough time has passed to enact their revenge? What dastardly plans have they got up their sleeves, or in their heads?

Actually, the real question is why haven't we seen poor old Mr Huffle since?