Oh it's easy to catch up.
There's three Crawley daughters - Mary, Edith and Sybil.
Mary falls in love with Matthew from the beginning...but, alas...it doesn't turn out.
Then she is swept off her feet by a visiting Mr. Pamuk...who visits her in her room. Needless to say he dies in her bed. Oh, the shame! She has her maid Anna and her mother, help get him out of her bed and carry him back to his.
Scullery maid Daisy sees this and eventually leaks this information to middle sister Edith, who has always had issues with Mary.
Matthew who loves but, for very many obstacles doesn't hook up with Mary....eventually gets involved with Lavinia. Sweet girl. He goes to war, comes home crippled and she's still by his side....well, on his left side, because Mary is on his right, as he's recuperating in their home, Downton Abbey. At the end Lavinia sees Matthew and Mary share a kiss....and the next day she gets the Spanish Flu and dies. Out of guilt Matthew can't marry Mary, now.
Edith has fallen for an older gentleman, Sir Anthony...and to spite her, Mary tells Sir Anthony that Edith his having a hoot leading the old stooge along. He takes it to heart and leaves...and Edith is heart broken.
So, Edith leaks the information concerning Mr. Pamuk's demise to the Turkish embassy, and gossip reigns supreme. No eligible man will look at Mary.
To save face, Mary agrees to marry the newspaper tycoon who is harsh and mean and domineering. At the end of Season 2, Mary's father finds out why she's marrying him and tells her to call of the wedding, that they will get through the gossip.
End of Season 2, Matthew proposes to Mary.
and they finally wed
Youngest sister Sybil, is a rebel....she's all for women's rights, etc. Falls for the Irish chauffeur, Branson....and eventually marries him and moves to Ireland...to the shock and dismay of the entire family.
She's now back for Mary's wedding, and pregnant. Mary gets married and is happy....and Edith once again tries to make amends with Sir Anthony...whom her father deems an unfit match for his young daughter. Either way, they decide to wed....and at the altar, the old man realizes the error of marrying Edith and leaves her standing at the altar.....and Edith is once again heart broken and upset that youngest sis is married and pregnant and Mary got Matthew....and she's destined to be a spinster.
Lord Crawly made a bad investment and is about to lose the house, but, Lavinia's father died and left Matthew (dead daughter's almost husband) tons of money...enough to save the family from living a middle class life. Matthew and Mary go at it, because Mary is all about the money, but, Matthew feels it's deceitful, because he broke Lavinia's heart and then she died. In the end, he takes the money and the rich remain rich.
There's a great storyline downstairs, as well. Anna and her Mr. Bates who is in jail for killing his ex....which he swears he did not...and because we love the two of them, we believe him.
Then there's Mrs. Obrien and Thomas the footman, butler or whatever he is now. They were in cahoots and made life miserable for all the servants...she even was the reason that the Lady of the manor slipped on a wet floor and miscarried. However, the two are at odds these days and trying to destroy each other.
Then there's the scullery made/cook's assistant Daisy, who led on William the footman....he fell madly in love with her, but, she didn't love him back apparently. Then he went to war, and everyone told her to play the part of his sweetheart to keep his spirits up. He came home mortally wounded and she was talked in to marrying him, so he dies happy....and he wanted to marry her so she would get a widow's pension. Now his father shows her fatherly attention and she feels guilty....but, she's starting to like having a father...
....plus, countless other little story lines.
Love Cousin Violet and her one liners.