写一段关于《波尔达克 第四季》的内容简介，要求简介明了，不能剧透，介绍内容包括主要演员、背景等，并且能够吸引读者兴趣
Ross (Turner) must defend Cornwall from an empowered George Warleggan (Jack Farthing), and risks everything he holds dear as he embarks on a political journey which takes him to the nation's capital. Demelza (Tomlinson) finds her loyalties torn, Elizabeth (Heida Reed) tries to strengthen her marriage, Morwenna (Ellise Chappell) continues to be oppressed by husband Reverend Ossie Whitworth (Christian Brassington), and the Enyses (Luke Norris and Gabriella Wilde) are tested as never before.