Korra Season 3

I'll summarize it the best way for you. But you should really watch episodes 7-14.
Dark spirits started to appear along the Southern Water Tribe and quite a bit has changed; Mako is an officer working his way to becoming a detective in the Force, Bolin holds leadership of the Fire Ferrets team without Korra and Mako, then Asami is trying to keep her company alive after what her father Hiroshi has done. While Tenzin was interested in continuing Korra's air-bending and Spiritual training by taking her to the other Air-temples, she feel's that she no longer needs to improve. Before they start their trip, Korra mentions the Glacier Spirits Festival and everyone comes along. While it may seem that Korra and Mako are a good couple, a lot of negativity builds up as they are not very good at reading each other's support. Upon arriving, Korra's family is reunited and the Northern Water Tribe arrives; their chief Unalaq and his two children get off the boat and the greetings between Unalaq and his brother Tonraq isn't friendly. At the Feast, Unalaq opinionated the lack of spiritual appreciation that the south has and later on feeds information in regards to Korra's isolation. He explains that the Avatar should have the freedom to see the world and chose their masters so that they could grow to be wise and diverse; pointing his fingers at Tonraq and Tenzin for that. This upsets Korra as she was under the impression that it was Avatar Aang's decision. Shortly after the Festival a powerful Dark Spirit attacks Korra and nothing could stop it until Unalaq used a spiritual bending technique using water to convert it's energy from Dark to Light. Proving his worth to Korra as a spiritual mentor, she decides to learn from him. Tenzin and Tonraq refuses Unalaq's involvement with Korra, but this further convinces her that she needs to end her training with Tenzin and dismiss him. Things turn for the worse as the dangerous Everstorm Blizzard is coming and that the only way to stop it is to open a Spiritual Portal to clear the storm and allow the Southern Lights to appear with the spirits dancing in the sky. Korra learns of her Father's past involving the destruction of the Northern Water Tribe's spiritual forest that surrounds the Norther Spiritual Portal and how angered spirits attacked the capital, eventually leading to his banishment and allowing Unalaq to take the throne. Upon opening the Southern Portal a great light also appears around a particular wooden statue in the Southern Air Temple that Jinora has been drawn to. Korra is thanked and congratulated for opening the portal. When Bolin hugged Korra, his love interest Eska (Korra's cousin who has a twin brother named Desna) shows some possessiveness.

To make a long story short at this point (I'm only going up to episode 6):
Unalaq begins to enforce the Norther Water Tribe ways among the people of the South with his Army, the citizens do not take lightly to this and Varrick, the Southern Water Tribe's eccentric billionaire entrepreneur that Asami was opening a deal with convinces the political powers to prepare for a rebellion, Korra tries to ease the situation suggesting that they should reconsider allowing the South to reconnect with their sister tribe and learn more about spirituality from Unalaq. This does not work and an attempt to kidnap Unalaq (which was stopped by Korra) leads to the arrest of the assailants and eventually her parents. Although her mother was released, Tonraq was given a life sentence. Korra is angered by the judge and decides to change his mind with death threats. When she held him between Naga's jaws, he explained the truth about Unalaq and his involvement with Tonraq's banishment. By releasing her father with the help of the Krew, it was official that the Water Tribes are at war and while the South is under the North's mercy, they would need some Naval help. As soon as the Krew arrived, everyone has split to work on their own problems except for Bolin. Republic City's President; Raiko refuses to help Korra and Varrick suggests to bypass the President's authority and go directly to General Iroh. Although he was willing to help, President Raiko catches them and threatens Iroh to Court Martial if one ship leaves the port. Apparently Mako has ratted Korra out when he was struggling with propaganda's that points fingers at Norther Water Tribe people when the Southern Water Tribe Peace Rally was attacked. Meanwhile, Bolin begins to work with Varrick as a Mover/Actor for a film series called 'Nuk-Tuk' after Mako abandoned him as soon as they arrived to Republic City. The fame gets to his head and he returns the favor to Mako. Everything blows up between the Krew as Korra nad Mako's relationship fell apart due to their conflict of duties/responsibilities. After their breakup Korra decides to head to the Fire Nation by herself to get support. Unfortunately, she is attacked by her cousins Desna and Eska (Eska is out to kill Korra for being responsible for ruining the wedding she was forcing upon Bolin), in the middle of their fight an enormous Dark Water Spirit attacks Korra, though she was getting close to utilizing Unalaq's Spiritual Bending Technique on it, she was not able to pacify it and ends up being engulfed despite launching a large pillar of flame back at it. Back in Republic City, Asami's shipment of Mechs to the Southern Water Tribe is being intercepted 'supposedly by Nothern Water Tribe activists' and with the help of Mako, they pull a 'Sting Operation' to attempt a capture of the real culprits. Mako has been working very hard on trying to find the true culprits behind the attack on the Peace Rally and now the intercepted shipments. Sadly the operation went foul and Asami is on the verge of losing the only thing left of her family: 'Future Industries' and she falters into Mako's arms for emotional support, this rekindles their relationship and this upsets Bolin because Mako's breakup with Korra was just a week ago. Despite finding evidence to prove that the Northern Water tribe is not the culprit and that it was actually Varrick, he was framed and taken to jail immediately. When Korra is found laying unconscious on a beach disheveled and confused, Fire Sages attempt to help her only finding that she is without her memories and a corrupt soul that will eventually kill her.

PS: I recommend watching episodes 7-14 to finish the season.