The Diplomat season 3 recap: Everything you need to remember ahead of season 4

The Diplomat is back for season 4, and audiences have been counting down to the return of one of the sharpest political thrillers ever made.

In the era of shows being quickly cancelled, the fact that Debora Cahn's series has made it to a fourth outing proves just how good it is - and we can't wait to re-join Kate and Hal Wyler, and President Grace Penn and Todd Penn, to see how they handle the aftermath of the potentially catastrophic decisions made during season 3.

But if season 3 seems a long time ago now and you need to refresh your memory about just what went down (a lot, and it was all gripping,) we've put together a handy recap with everything you need to know, all in one place.

The Diplomat season 3 recap

The first key and shocking plot point from season 3 was Margaret Roylin's death. The fallout from her demise is felt throughout the season, and she died as a result of her role in the HMS Courageous explosion.

Across seasons 1 and 2, Kate realised Margaret's part in the explosion and the following cover-up, and by season 3, Prime Minister Trowbridge also found out about her connection to the attack.

Margaret was offered asylum in America, but instead of further betraying her country, chose to take her own life at the end of episode 1.

Grace Penn was also involved in the attack, and season 3 saw her become President when President Rayburn died. She entered the role knowing she had a part in setting the attack in motion, which killed 43 people, and dealing with her feelings about it.

She believed the tragedy would maintain the strength of the UK and ensure America’s nuclear safety along with it. She felt guilty for what she did, but still ultimately stands by the feeling she made the right choice.

Kate decided the best way to handle the aftermath of the attack was to pin it on President Rayburn, as he was no longer alive to defend himself.

When Grace entered the White House as the new president, another huge storyline, and one fans are unlikely to have forgotten from season 3, unfolded: Kate was overlooked for a massive promotion which ultimately went to Hal.

Kate was the frontrunner for the role of Vice President and in a shocking move, Grace chose Hal for the role.

This was largely because his ruthless decision making and unsanctioned diplomacy aligned with her own style of governance. She believed he could strengthen her administration, despite Kate being the best person for the job.

Kate responded to this news by agreeing to be Second Lady publicly, while deciding to privately stay in London as ambassador rather than being side-lined as her husband's career flourished.

Prioritising herself, she not only wanted distance from her husband, but also from the harsh burn of being overlooked for the Vice Presidency. Kate also kept her role in the Foreign Service because she passionately believed there was still plenty of work to be done in London.

Separated both by distance and also emotionally, Kate embarked on an ill-fated attempt at a dalliance with Foreign Secretary Dennison, and a full-blown affair with intelligence officer Callum Ellis while away from Hal in the British capital.

Kate and Hal weren't the only ones having marriage problems, with Todd also seemingly unhappy in his role as First Gentleman - he grew suspicious of whether his wife could be having an affair with Hal with little to do but be jealous of the time they spent together.

Todd adores his wife, and while there was nothing going on between her and Hal, they have a professional dynamism and similar sense of humour that exudes chemistry to anyone seeing them together.

He felt threatened that his wife could be fulfilled by someone else, even if it isn't romantic in nature - his paranoia resulted in childish behaviour when it came to the working relationship Grace had with her colleague.

Next up is something that is crucial to remember before watching season 4, and that's the Poseidon missile debacle.

Callum Ellis revealed during season 3 that a nuclear weapon called the Poseidon was on a Russian submarine submerged just off the English coast. Prime Minister Nicol Trowbridge formed a plan to work with China to remove the submarine, a decision Grace argued heavily against.

Hal and Kate, deciding to give their marriage another go by the end of the season, convinced Trowbridge to get the US on board to get rid of the weapon, rather than collaborate with China. The plan was for the Poseidon to be buried under the sea and caged in concrete, but it was stolen before anyone could get to it.

While the theft was blamed on Russia, Kate worked out moments before the end of the finale that it was actually Grace and Hal who had stolen it - this will not end well for the newly reunited couple.

It turned out the President and vice President wanted the torpedo for themselves because they didn't want it falling into the wrong hands, even though the decision to take it could already have dire political consequences.

But having such a potentially catastrophic weapon to be used for American intelligence was an opportunity they couldn't pass up, despite their actions pushing the UK and US the closest to war they've ever been.

We can't wait to see how the fallout from this is handled during season 4.

The Diplomat season 4 airs on Netflix from October 14.