Why do Percival and Fosco switch Laura’s identity?

They need Laura’s money without her person. Percival is secret-heavy debt; murdering Laura outright is risky, but declaring her dead while Anne Catherick’s body stands in for hers lets him inherit and remarry freely. Fosco engineers documents, asylum records, and witnesses so “Laura Glyde” dies on paper while the real Laura is drugged and imprisoned as Anne.

The swap exploits resemblance and sexist law: a confused woman in an asylum has no voice. Marian and Walter must prove continuity of memory, handwriting, and love — not just a face. The plot is therefore about property and erasure, not gothic randomness. Anne’s earlier confinement rehearsed the machinery applied to Laura.