The underlying plot was good and I thoroughly enjoyed the first couple of episodes but then it descended into a typical holywood hostage thriller with a leaderless bunch of people with every tragic back story under the sun bawling and fighting with each other. Off the train and at operation HQ weak characterisation and totally unbelievable unprofessional senior police officer and head of GCHQ scoring points off one another and the the poorly characterised head of cyber security and her undermining deputy. Made matters worse and even turning this tragedy into a comedy. All this of course was capped by the now essential lovey dovey talks between the key characters charged with preventing disaster while the runaway train hutled to its doom and seconds ticked away. A good plot, as I say but a far better thriller could have been contrived in half the number of episodes.