Jarndyce (Denis Lawson) brings Mrs Rouncewell (Anne Reid) to her son, Sergeant George (Hugo Speer), and they're reunited in his cell.
She pleads with him to use a lawyre. Eventually he relents, on condition that his brother is not involved. Their old rivalry still won't let him swallow his pride.
Inspector Bucket (Alun Armstrong) continues his investigations, after receiving a poison pen letter pointing the finger of suspicion at Lady Dedlock (Gillian Anderson).
He interviews Mercury (Richard Cant) about Lady Dedlock's movements on the night in question. But the footman can't quite place what Lady Dedlock wore for her night walk, as she has so many clothes.
Above stairs, Mrs Rouncewell pays an unexpected visit to the Dedlocks' London house, where she begs her mistress to help George. She hands over a letter which was delivered to her at Chesney Wold. Alone, Lady Dedlock opens it. It reads 'Lady Dedlock Murderess'.
Elsewhere, Woodcourt (Richard Harrington) and Richard (Patrick Kennedy) have become good friends. Woodcourt talks of his envy of the love Ada (Carey Mulligan) holds for Richard. He wishes he had the same from Esther (Anna Maxwell Martin), and reveals his intention to propose to her soon.
Next day, Esther and Ada pay Richard a visit. Esther is surprised that Ada seems to know the way there. Richard greets them warmly but is clearly very unwell. Esther is devastated to learn that Ada is not going back with her. She and Richard have married in secret, and she is staying with her husband.
Inspector Bucket's investigation gathers steam when he identifies the mysterious letter-writer as Hortense (Lilo Baur). As evidence mounts against Lady Dedlock, Bucket sets a trap for the killer - which results in the arrest of Hortense for the murder of Tulkinghorn (Charles Dance).
Screenplay by Andrew Davies.
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