Agents of SHIELD
The Agents of SHIELD principal cast. Marvel Studios

Agents of SHIELD disappointed a lot of people when it first started in the autumn of 2013, but after a slow, problematic and often terrible start the show finally built itself into a fine companion to Marvel Studio's increasingly-popular movie franchise.

As thoroughly-entertaining as the ABC show was during its final run of episodes – starting around the release of Captain America: The Winter Soldier and closely tying into its events – it was only ever recommended viewing, not essential.

That changed with season two. With the characters all set-up and the cast expanded with new bit-players who have already endeared themselves better than Skye, May and Ward did at the start of season one, the show has been in exceptional, flying form.

It has been brilliant week in and week out. Even the worst episodes of season two have been better than the majority of season one. This has been thanks to a tighter focus, a lot more salacious darkness and a story that has readily answered a stream of mysteries – giving the show a sense of purpose and enticing people to watch with the promise that plot points will carry from episode to episode.

WARNING: Spoilers for Agents of SHIELD season two – up until episode 10 – follow.

The core storyline has concerned the source of Agent Coulson's (Clark Gregg's) revival following his apparent death in Avengers Assemble. He was brought back thanks to an injection of a substance known as GH.325 – which as we discovered last season is derived from an alien corpse kept secret by SHIELD.

As revealed in episode nine that alien was a Kree – blue-skinned beings which debuted on the big screen in Guardians of the Galaxy. The serum gave Coulson visions, sending him into a trance which revealed etchings marked into any surface he could find. He later worked out those etchings were a map, a map of a hidden city.

All this as SHIELD and villainous group HYDRA fought over possession of The Diviner (or Obelisk) an alien artefact that turns people to ash... unless they happen to be "worthy" as the girl in the flower dress, aka Raina (Ruth Negga) is and Skye (Chloe Bennet) is alleged to be as well.

What happens in the mid-season finale?

Agents of SHIELD
Skye (or Daisy) after her powers are unlocked. ABC

In last night's (US pace) episode ten we discover not only that Skye is in fact Daisy Johnson from the Marvel comic lore and her father (Kyle MacLachlan) is Calvin Zabo, aka Mr Hyde but also that Skye and Raina both have powers unlocked by the Diviner's activation.

This unleashes the Terrigen Mist – a mineral that unlocks latent powers in humans thanks to the tinkering with our DNA by the Kree centuries ago. In the comics this creates the Inhumans – a new species of human with devastating powers.

The Inhumans are coming to Agents of SHIELD, but they're also getting their own film in 2018 and which also happens to be the final film before Marvel Studios entire work to date reaches its conclusion in Avengers: Infinity Gauntlet Part. Safe to say then, that what AoS is doing now is VERY important to the Marvel Cinematic Universe (MCU).

What does this mean?

With three and a half years left until the release of the Inhumans film, the fact the story is being started so soon is of huge importance, and probably means that the Inhuman race will be a factor in all Marvel films moving forward.

Essentially they will be the MCU's equivalent of X-Men's mutants – which they can't reference because of rights issues. These are individuals with powers who will probably be feared and shunned by humans without abilities.

How far Marvel take this we don't know – but it makes sense for Inhumans to figure in 2016's big film Captain America: Civil War, as it increases the need for that story's "Superhuman registration act" – which is at the centre of the dispute between Captain America and Iron Man.

That film will coincide with the end of Agents of SHIELD's third season. Its second will finish with Avengers: Age of Ultron, which it will also tie into, bringing us to two new characters introduced in that film: Quicksilver and Scarlet Witch.

Avengers: Age of Ultron
Aaron Taylor-Johnson as Quicksilver and Elizabeth Olsen as Scarlet Witch. Marvel Studios

As seen at the end of Captain America: The Winter Soldier – this brother and sister pair are in Hydra's control and are being experimented on. Either this is because they had their abilities already, or because Hydra unlocked them in a similar way the Terrigen Mists did with Skye/Daisy – making the pair Inhumans as well.

That appears to be where Marvel are heading, and the introduction of Inhuman characters on a smaller, television level gives them more soldiers for either side of the Civil War that will unfold in 2016 – if that's where they choose to take this.

What next?

Wherever this Inhumans plotline takes Agents of SHIELD it will be exciting to watch unfold, which is exactly what the show needed so badly in season one. The show doesn't return for the concluding episodes of season two until March, but in the meantime there's a new Marvel show to keep us occupied: Agent Carter.

Dealing with the setting up of SHIELD and their early post-war interactions with HYDRA, the show will star Hayley Atwell as Captain America's former love interest Peggy Carter. Quite how it will tie into Agents of SHIELD remains to be seen, but we'd be shocked if it didn't have close ties to where the show is heading once it returns.