The episode is called Vodka as you might need a lot of it to stay awake or stoop to a slumber after it has finished.
Anthony Blunt is feeling the heat as innuendos are made to him being a Russian spy. Nicholas Elliott even giving him a veiled threat in order to make Blunt panic.
The CIA contact Lily, to work with them officially or unofficially. They regard Nick as a weak link. They just cannot overlook his closeness with Kim Philby.
In Russia Philby gives Guy Burgess a punch. He ruined everything by fleeing to the Soviet Union, Burgess placed everyone else at risk.
Philby also finds out that the KGB do things differently as they kill someone who could had been ansset.
The lethargic pace just does not help. The story is not dense or complicated but they just want it to be Le Carre and the material does not justify it.