In “Serious Sweet,” her eighth novel, she burrows deep into the lives and minds of two anguished but sympathetic misfits as they ricochet separately around London over the course of a particularly fraught 24-hour period that keeps throwing up obstacles to their meeting. If that sounds grim, rest assured that this agonizingly penetrating novel is at heart an oddball love story that features what is probably Kennedy’s most hopeful ending yet. The novel’s 24-hour time frame and multifaceted portrait of the city in which its two protagonists live and work evoke James Joyce’s “Ulysses” and Virginia Woolf’s “Mrs.