(Spoiler***) The best part to me: Alex's experience at Billy's house of trauma (my title). She cleans his mom's house and uncovers links to trauma there which leads to her own long repressed, trauma. She connects much together, asks her dad questions about a cabinet (Alex and daughter are staying with father and his 2nd wife). The father lies to her which gives us an idea of where his character actually is at this point in time. Some comments on this board condemn her for not staying at her dad's. I thought the same initially.
What Alex experiences and is shown clearly in this part of the series is her experience of the "past literally happening in the present." It is a powerful psychological event that can actually occur. The insight is intense. The past is experienced in the present in an insightful experiential way. Not a "memory"...literally experiencing the past in the present.
Add that her father lied about the cabinet to her in the present and it makes perfect sense why she fled in a panicked state...and why she didn't stay there to begin with (although real reason not clear to her or viewers). It also provided insights to her about her mother's actions in suddenly uprooting Alex and herself so long ago.
Great acting and excellent psychological work on part of writers, etc. Superb, in fact.