Look at this:
By a stranger was kissed Chelsea.
You may well ask with some justification: Is "By a stranger" not part of the VP? It should not be, some may say, because it precedes the passive auxiliary. The question rightfully arises: What happened that "by a stranger" is part of the VP no more? How can we account for that? Or is there some inconsistency in TG? No, there is not.
The rearranged sentence is the result of two constituent movements:
1. NP (Chelsea = subject) extraposition
2. PP (by a stranger = adjunct) topicalisation