MI5 agent River Cartwright messes up a major anti-terrorism training exercise to the extent that if it had been an actual attack several hundred people would be dead or injured. He is banished to Slough House, the department where all disgraced MI5 officers are sent. Running the department is Jackson Lamb who, while hardly the epitome of an MI5 officer himself, runs a tight ship and has his staff doing all manner of meaningless tasks. He is trying to get them to quit.
A great start to the series. The opening scenes are fantastic and show us what we all expect MI5 and other intelligence agencies to operate. After that we have the purgatory of Slough House - far less glamourous, making for a great contrast.
While the main aim of this episode is to meet all the main characters, it is very interesting and engaging. There is some humour to lighten the mood.
There is also some cloak-and-dagger stuff and an actual threat, so not all scene-setting but also some intrigue and action.