Brideshead Revisited Steaminess Rating

Exactly how steamy is this story?

PG-13

We're rating this PG-13, but only because all the sex and alcohol-related words in Brideshead Revisited are at a level of vocabulary too advanced for those under the age of thirteen to understand. How can you pass up a novel with "Dionysian," "prurient," "dipsomaniac," "gerontophile," "roué," "licentious," "pederasty," "crapulous," "succubus," "siren," "louche," "jeraboam," and a dash of British sexual slang?