Pierre assents to both:
(1) London is pretty
(2) London is not pretty.
And, by stipulation, Pierre is rational--he doesn't let contradictory beliefs pass.
Options to resolve the puzzle:
(A) Reject disquotation: Though he assents to them, Pierre doesn't actually believe (1) or (2) (Marcus).
(B) Reject assumption of Cartesian access: Pierre can believe both without impugning his rationality if he doesn't have immediate access to sameness and difference of content (Owens, Brown).
(C) Adopt subjective senses: "London" has different senses associated with it in (1) and (2), so the associated contents of belief are different. Pierre is not irrational.
(D) Reject assumption of Cartesian rationality: Pierre is not perfectly rational. He holds two contradictory beliefs. Rationality is not completely the subject's responsibility: he can be irrational without recognizing it (Millikan). Thinking (with Boghossian, Owens, Kripke, others) that rationality is completely within the subject's control is another version of Quine's dogmas of empiricism: it represents a fundamental cleavage between the domain of rationality and the domain of empirical inquiry. Maintaining such a cleavage requires an unacceptably formal understanding of rationality. (Marcus argues plausibly against the rationality of someone who holds contradictory beliefs.)
There is luck involved in rational culpability just as there is luck involved in claims to know, and in the ethical assessment of actions.