The Warden follows the story of Mr Harding, a cleric who is warden of Hiram's Hospital, a charitable home for twelve men who are no longer able to work. A local man, John Bold, is campaigning against corruption in the Church of England. He challenges the high income that the warden receives from the hospital (as a result of increased profits over the years from the estate which supports it, the hospital has more income than the gentleman who set up the charity ever envisaged). He feels more of the money should go to the twelve men themselves. Mr Harding is a good man caught up in a scandal not of his own making, and wrestles with his conscience, his loyalty to the church, and the defensive stance taken by the Archdeacon, his son-in-law.
The Warden is the first, and certainly not the best book in the Barchester Chronicles series, but it does display Trollope's easy to read style of narration, and the subtle humour that underlies it. The storyline is perhaps a bit slower than in the later books, and some of the interesting characters have yet to appear. The series is written in such a way that you could probably pick up any of the books and enjoy them as a single novel. Having said that, I think you would miss something special if you don't read the whole series. It is the characters that he creates in their own unique setting that makes Trollope's work worth reading, and to follow their development through each book makes the whole series far more satisfying than just one book.
The other books in the series are Barchester Towers, Dr Thorne, Framley Parsonage, The Small House at Allington and the Last Chronicle of Barset.