Jane Austen first wrote Susan the novel that was to become Northanger Abbey circa 1798-1799. In 1803 she offered it to Benjamin Crosby and Son, publisher of London. Crosby bought the copyright for £10 but never published the book.
Circa 1816 Jane Austen brought back the copyright of Susan from Crosby via the good offices of her brother, Henry Austen for the sum of £10. Crosby relinquished all rights to the copyright and returned the unpublished manuscript to Jane Austen. It was only after the purchase had been completed that Crosby was informed that the author was in fact also the author of Pride and Prejudice, which of course by that date had been a considerable success.
Jane Austen prepared the manuscript for publication in 1816 but it was not published, by John Murray, until after her death on 18th July 1817. The first edition appeared in December 1817, though the title page recorded the date of publication as 1818.
Here is a link to the e-text of the novel, Northanger Abbey
Here are links to AustenOnly posts about Jane Austen and Bath
Here are links to AustenOnly posts about Northanger Abbey.