Firstly, 'the Gate' could be the Cadian Gate, but I reckon it is the 'Gates of Varl', an area heavily assosiated [sp?] with the C'Tan, which would lead to a Chaos/Necron showdown. It could also be the Lion's Gate spaceport, which is linked to the Holy Palace, like the Eternity Wall. Also, 'the Palace' could be, wait, IS, the Holy Palace on Terra, home of the Golden Throne, ergo, home of the false Emperor.