Witness for the Prosecution ending explained

What happens

After Leonard is acquitted, Christine reveals she faked her betrayal: she was the Cockney woman and wrote the letters. Leonard then gloats that he really did kill Mrs French, so Christine stabs him. Wilfrid agrees to defend her.

The last image

Wilfrid, shaken, takes up Christine's defence, and Miss Plimsoll helps him back into his barrister's role.

What it says

The acquittal looks like an answer but isn't one: a trial can end in a verdict without justice. Everyone has been performing, and love and manipulation are hard to tell apart. The twist shows how easily a room can be persuaded.