The narrator tells us he's received an invitation to a wedding in England, and since he can't attend, he sends this series of recollections about the bride as a wedding present.
Flash back to 1944 – the narrator is stationed in Devon, England, at a special, top secret military intelligence school.
It's the narrator's last day there, so he heads into town for the afternoon. He stops by a children's choir rehearsal in the village church.
There, he notices that one of the children is clearly the best singer of the bunch – a bored-looking young lady who doesn't seem thrilled to be there.
After the singing ends, the narrator goes to a tearoom and orders some tea and cinnamon toast (yum!).
The narrator passes the time by rereading some rather dull letters from his wife and mother-in-law.
The talented girl from the choir shows up, with a little brother and a governess in tow.
She makes a beeline for the narrator, and strikes up a conversation.
The pair chats about a variety of things, from the girl's plans for the future to the assortment of different Americans she's encountered (she's not always a fan). The narrator takes note of the girl's ridiculously large watch, and wonders about it.
The narrator finds out a few central facts: the girl's name is Esmé, she's a titled aristocrat, and her mother is dead.
Esmé's brother, Charles, runs up to the narrator. The narrator attempts to engage the little boy in conversation and fails.
The narrator observes this new addition to their table, who, in turn, gives him a huge raspberry.
The narrator explains that he's a short story writer – kind of. He agrees to write a story for Esmé someday.
Charles repeats a riddle he'd told earlier. The narrator, for reasons unbeknownst to us, says the answer before Charles can – not the best idea.
Charles storms off, and the narrator, concerned, watches him sulk.
Esmé has to leave, but first, she takes the narrator's address; they agree to write letters.
Esmé and Charles leave – the narrator is unusually "emotional," though we're not entirely sure what emotions he's feeling.
The children immediately return – Charles grudgingly kisses the narrator goodbye, and the narrator gets the little boy to forgive him by asking the riddle one more time.
The narrator reasserts his promise to write a story for Esmé.
A year or so later, the narrator informs us of our new surroundings – Gaufurt, Germany, just after the end of the war.
The narrator absents himself from the story, claiming that he's disguised as another character.
The disguise is easy to see through – the narrator is clearly Sergeant X.
Sergeant X is in a state of complete breakdown; he feels mentally and physically unstable, and doesn't do anything all day but chain smoke and read.
Sergeant X attempts to write a Dostoevsky quote in a book, but is horrified to see that his handwriting is actually indecipherable.
Corporal Z (whose name is Clay) shows up to chat with Sergeant X.
Sergeant X briefly talks to the rather inconsiderate Clay about X's various nervous tics; we learn that X was in the hospital because of a nervous breakdown.
X patiently listens to Clay jabber on about his girlfriend back home, Loretta. Apparently, Clay wrote to Loretta (a psych major) about X's breakdown.
Clay brings up something that's been troubling him since the war – he killed an innocent cat after a shell attack, and Loretta explains it as temporary insanity. Sergeant X, however, sarcastically and cruelly tells Clay that the cat was a German spy. We see how much X has changed because of the war.
X is sickened by his own response – literally. He throws up.
Clay tentatively makes a friendly overture, and tries to coax X into joining him and some other guys to listen to a radio broadcast. X turns him down, and remains alone in his room.
X tries to write a letter to a friend back home in New York, but finds that he's shaking too much to type. He collapses for a moment.
Listlessly, X opens a package that he finds on his desk – it's apparently been trying to track him down for a while, and has a bunch of his old addresses on it.
X reads the letter, which is from Esmé, and finds her father's watch included in the package.