Chaos is a Ladder.

We'll get to Littlefinger and Sansa...

But first, Jon Arryn.

The show opens with the death of Jon Arryn, he was a head of House Arryn whose titles included Lord of the Eyrie, Defender of the Vale, and Warden of the East. He served as Hand of the King to Robert Baratheon from 283AC until his unexpected death in 298AC.

Jon fostered Eddard Stark and Robert Baratheon as his wards in the Vale of Arryn. As they grew, the two boys became close companions and regarded Jon as a second father. After King Aerys II Targaryen demanded that Jon turn them over for a likely execution, Jon refused and raised his banners in revolt.

Jon's quick health decline and death would seem suspicious to those who cared the most about him, Ned and Robert

King Robert Baratheon decides that Lord Eddard Stark should succeed Jon as Hand of the King, which angers both Queen Cersei Lannister, who had hoped her brother Jaime would assume the position and fears that Eddard would move to curb Lannister influence.

Lysa writes a coded letter to her sister Catelyn, in which she claims that Jon Arryn was murdered by Queen Cersei. This convinces Catelyn and eventually Eddard, who had been inclined to refuse King Robert's offer, that he must assume the position of Hand, so that he can find out the truth about Jon Arryn's death and expose those responsible

Jon was seeking further proof that Cersei's children could not be Robert's in Grand Maester Malleon's book The Lineages and Histories of the Great Houses of the Seven Kingdoms, a ponderous tome lent to him by Grand Maester Pycelle. The book would have informed him, as it later informs Lord Eddard Stark, that whenever members of houses Lannister and Baratheon wed, their offspring always bore clear Baratheon features[2][12] (unlike Cersei's children Joffrey, Myrcella, and Tommen, who more closely resemble the Lannisters). Jon's investigation became known to a number of people at the court, including Pycelle, Varys, Cersei, and Littlefinger. Varys saw Jon's life in danger and begged him to employ a taster, but Jon dismissed the suggestion that anyone would try to poison him

When they were young, Catelyn and Lysa first learnt to kiss by taking turns kissing Petyr. Catelyn recalls it being very innocent, though Petyr was more forward with Lysa, who allowed him to kiss her with tongue. During this time, Lysa fell in love with Petyr, but her feelings were not reciprocated. One night Petyr tried to kiss Catelyn, and she rejected him, laughing. Petyr got drunk because of this, and Lysa climbed into his bed that night to "give him comfort". Petyr took her virginity that night, telling her he loved her, but called her "Cat" before falling asleep

When Catelyns wedding date to Brandon Stark was announced, Petyr challenged him for Catelyn's hand[4].. Brandon wounded Petyr severely and Lysa offered to nurse him. In the following fortnight, they slept together again. Lysa became pregnant with Petyr's child as a result of this[3]. After Hoster had send Petyr back to the Fingers, Lysa revealed her pregnancy to him, in the hopes that Hoster would relent and let her wed Petyr, but Hoster forced her to abort the child instead

We all see how Petyr has looked at Sansa since they first met, she reminds him of a young Cat

Lysa meets him there and insists upon marrying him on the spot. He reluctantly agrees.

She reveals that Petyr had convinced her to poison her previous husband, Lord Jon Arryn, claiming it was to prevent him from sending her young son Robert away to be fostered. Lysa, who was fiercely protective of her son, did his bidding. She also reveals that after Jon was killed, Petyr convinced Lysa to write a letter to her sister Catelyn stating that Lord Arryn had been poisoned and that the Lannisters were responsible.

"Littlefinger was born with no lands, no wealth, no armies," "He has acquired the first two: how long before he has the army?"

So, now we start to see the grand plan Litterfinger has been working on, which leads us to another question, What is Varys up to and what is his grand plan? ...for the Realm...