Line of Duty: who is 'H'? What we know about mystery that kept viewers guessing The search for H has been at the core of the eventful series which started in 2012 The video will auto-play soon8Cancel Play now Want the best food, film, music, arts and culture news sent straight to your inbox?Invalid EmailSomething went wrong, please try again later. Sign up for regular updates of events happening in Wales When you subscribe we will use the information you provide to send you these newsletters. Your information will be used in accordance with ourPrivacy Notice. Thank you for subscribingWe have more newslettersShow meSee ourprivacy notice