The previous episode ended with Strike trying to revive Rochelle Onifade, who was drugged and drowned in her own home. The episode starts with Strike following up the case with Detective Eric Wardle, the detective in charge of the Lula Landry case. He and Robin thinks that the killer is the same person for both women. Strike then informs Landry's crew of Onifade's demise. This included Ciara (a model friend), Guy Some (designer) and Evan Duffield, Landry's boyfriend. Strike's presence at a party causes Evan to be skittish, but drops by his office the following day to see if he is still a person of interest and to give information about Freddie Bestigui. Strike and Ciara also discuss Landry's closeness with Onifade, how she was helping Landry with knowing her identity.
Strike also follows up with his suspicions regarding Tansy Bestigui's testimony, and finds out that she rescinded her previous testimony to protect her husband's image. She did hear an argument but could not identify the other voice. He has also revealed that the doorman was not on his desk, thus someone could have entered the building without his knowledge. This led Strike to investigate the vacant flat below Landry's, and to look back at the CCTV footage of the grounds on the night of the murder. An important discovery is that someone was in that vacant flat (not the supposed tenant) based on visual evidence - something from the vacant flat was found in Landry's apartment. Another is that, while there was someone loitering around the area on the night of the murder, the person on camera were two different people - and one of them was the murderer.
I think this last bit may be a red herring, but I don't remember much from the book so this might be important. In a small part of the episode, Strike meets up with John Bristow and his mother. His mother mentions that Landry is frightened of someone, but her statement might be made from delirium due to her medicine.
Adaption-wise, this is faithful to the book. The key elements are there, and I think it's what matters here. This episode is also an info dump on where the narrative is supposed to go. Statement of events are given, and more people are held under suspicion that they may be the murderer. If I remember correctly, the killer may already be on play, but the motive is still unexposed.