The Old Curiosity Shop tells the story of Little Nell, a beautiful and virtuous young girl who lives with her grandfather in his shop of curiosities. Her grandfather loves her dearly, and Nell does not complain, but she lives a lonely existence without friends of her own age. Her only friend is Kit, an honest young lad who works at the shop, and whom she is teaching to write. Unbeknownst to Nell, her grandfather is obsessed with their precarious financial position and is attempting to make Nell a good inheritance by winning at cards. He keeps these nocturnal activities a secret, but borrows heavily from the evil Quilp, a dwarf, in order to raise new capital. In the end, he gambles away what little money they own, and Quilp seizes the opportunity to take possession of the shop and make Nell's and her grandfather's lives a misery. Indeed, her grandfather suffers a breakdown, which leaves him bereft of his wits. Courageously, Nell decides to escape Quilp, and she and her grandfather run away to the country to live as beggars, travelling into the Midlands of England.
There, then, follow the multifarious adventures of Nell and her grandfather, Quilp and his sly minions and accomplices, who would be Nell's vehement pursuers throughout the entire story, the noble schoolmaster, and many, many other personages as bright and memorable as Dickens' heroes always are. But... let us hear the story itself, shan't we?

(Description from Wikipedia with additions by Euthymius)