At the end of the third episode, Julia's PR aide Tahir Mahmood steps onstage as Julia she implies in a speech that she's got her sights set on being the Prime Minister. As Tahir does so an explosion rips through the room which leaves the Home Secretary's fate uncertain.
And it's not until the fourth episode that it's revealed that Julia died during surgery in an attempt to save her life. Weirdly she dies unceremoniously off-screen. Or did she?
One theory is based on Romeo and Juliet, with the Secret Service and the Police being the basis of the two warring houses. Julia Montague is a modernised version of Juliet especially when her relationship with David is extremely forbidden and he even attempted suicide in episode 4 when he assumed that Julia had died. It's hard not to see the comparison to the Shakespearean tale...
But even if the plot isn't taken from Romeo and Juliet there's plenty of other reasons why Julia could have faked her death. David's family had been made targets because of his connection to her and she had also endured a gruelling assassination attempt. Going into hiding would throw any would-be attackers off her scent but since she also has plenty of opponents within Parliament, the Police and the Secret Service, this could also draw out any political enemies that she can keep an eye on.
And if Julia's still aiming for the Prime Minister's seat what better way to get the public on her side than by gaining their sympathy? She survived a public assassination and had to go into hiding to protect herself.
Plus, look at it from a creative writing point of view; by the third episode, the relationship between Julia and David had truly intensified and they were in the middle of a dangerous affair. Why would Jed Mercurio (the creative mind behind the show) deny the opportunity to have an emotional goodbye between the two?