Is Ruth Insane AND [SPOILERS]?
I rewatch this film more times than I'd probably admit. I rewatch it for several reasons, among which is trying to figure out the animus toward it, toward the plot, and toward Ewan McGregor's character (or McGregor himself).
To say that it isn't "Chinatown" seems invalid, in respect to the fact that it and other recent noir films share very similar protagonists, none of whom are even hinted at being as individual as Jake Gittes is. "Michael Clayton" and "The American" (not to mention other late '00's foreign noir films) show men either of flimsy conviction, dubious morals, or characters lacking in depth--but getting into situations that test whether they will mature morally.
Having said that, and aware of the foul IMDB board posters who routinely come here to bash (beautiful) Olivia Williams, I found myself wondering if the whole mystery-CIA-car-of-death thing isn't related to Ruth Lang and to Ruth Lang alone. From first to last, this character complains about imaginary or real adultery by her husband, about her lack of parity with Amelia Bly in the looks department (and even with Cambridge coeds back in the day), and with the fact that a guy who sleeps with her wishes she had been gone in the morning. In fact, hers is the only character invested with depth; and so finally I wondered if she's just not plain crazy, and if the CIA-agent identity isn't a red herring.
It's true that some sinister government agency could have wiped out the Ghost at any time prior to the book signing. It's true that the Ghost isn't the brightest of writers (while, however, being one of the more empathetic and understanding), and that it's likely his presence at the book-signing may have been speculated upon by sinister government types, at which time a hit would be just terrible; and not at all connected with sinister government types .
On the other hand, it's possible that Ruth Lang is just plain crazy, and that, no longer in any position of power, and reduced to the role of wife that she herself deems insignificant, she has the car-of-death ready for one last shot at notoriety. She's a particularly malignant individual who sets up her husband for the exact type of fate that befalls him (even though she apparently has nothing to do with the bereaved father's act at the airport, at the end). She just hates her husband's guts, is histrionic, and an all-around termagant.