But then we sit down, and all traces of fractiousness disappear. Adichie is fun, polite and thoroughly likable. She is manifestly serious - about her writing, about the world - but what's most engaging about her is that she doesn't seem to take herself, or anything else, too seriously. A streak of mischievous humour runs through everything she says - and when this breaks out into laughter, as it frequently does, she really goes for it, her whole body shaking as she chuckles.
So easygoing is Adichie that it's easy to forget what a big deal she is. Her first novel, Purple Hibiscus - a coming-of-age tale about a 15-year-old Nigerian girl and her struggles against her repressive father - was published to acclaim in 2003. But it was her next book, Half of a Yellow Sun, that made her a sensation. A hugely accomplished and harrowing drama about the Biafran war, the novel won the 2007 Orange Prize and went on to sell 650,000 copies in Britain alone. Last year she was awarded the prestigious - and lucrative - MacArthur "genius" scholarship, which, she says, has given her the freedom to move between America and Nigeria and to concentrate, for the first time ever, solely on writing.
Adichie, 31, is in Britain to promote her third book, and first collection of short stories, The Thing Around Your Neck. She has been writing the stories for years - the earliest, she tells me, dates from before she began Purple Hibiscus. She describes the process of putting the collection together in a typically jokey way. "My editor really selected them. There were some I wanted and she would say, 'No, this isn't right, blah blah blah'. And I remember looking at them and thinking, 'I hate every single one!' I would email [my editor] and say, 'Why would anyone publish them?', and she'd say, 'Chimamanda, calm down.'"
Her editor's advice was sound, because the stories in The Thing Around Your Neck are superb. With minimal fuss or apparent effort they present snapshots of Nigerian life. Some take place in her homeland but most are set in America - a departure for Adichie, since both her earlier books are set wholly in Nigeria. But, as she points out, she has spent much of the past decade in the US, so it's not surprising that the country should have found its way into her fiction.
Having said that, the stories don't give the impression that she is too enamoured of the place. The lives they depict are unremittingly bleak; these are parables of disappointment, studies in how crushing immigrant life can be. One is about a woman forced to live alone in America while her husband installs a mistress in his house in Lagos (in Nigeria, apparently, having a wife in America is a sign of status). The title story tracks the life of a young woman sent to the US by her family in the expectation that she will send back "handbags and shoes and perfumes and clothes". After the uncle she initially moves in with molests her, she flees to Connecticut and takes a low-paid waitressing job. It is memorably, heartbreakingly sad, especially when it becomes clear that the object of the title - the "thing around your neck" - isn't something ornamental, but the choking loneliness the woman feels at night.
When I suggest to Adichie that her work doesn't display much affection for the US, she seems nonplussed. "I spoke to an American woman just before I came here and she said the same thing: 'From the stories, I don't think you like us very much'. I thought: What! I do, I absolutely like America. But it's a complicated affection, an affection that is very willing to criticise. There's a sense sometimes that because you're an immigrant you should shut up and be grateful that we let you in. But I think that's rubbish."
This comment, exacting but measured, is typical of Adichie. Both as a person and as a writer, she is engaged in an ongoing project of rebellion against the expectations of others - of those who want to be able to tell her what the world is like, and what her place in it should be. In this respect, her background is significant. Adichie grew up in the Nigerian university town of Nsukka, one of six siblings in a middle-class family. Both her parents (who are still alive) worked at the university - her father as a mathematics professor, her mother as an administrator. The family lived, by sheer coincidence, in a former home of Chinua Achebe, Nigeria's most famous novelist. But, Adichie says, they weren't especially bookish, and she says that her early interest in literature (she started off reading Enid Blyton) set her apart from her siblings, and made her decision to become a writer more acceptable to her parents.
Even so, she spent a time in Nigeria studying medicine ("if you were from my background, that is simply what you did") before dropping out and moving to America, where she completed a humanities degree. She subsequently did an MA in creative writing at Baltimore's Johns Hopkins university, and has since taught creative writing in the US and in Nigeria.
This unusual background gives Adichie a dual perspective on the way systems of power operate. On the one hand, she is a woman who grew up in a patriarchal society (albeit in a liberal family), and so understands how men can shackle women. On the other hand, she is an African who, having partially migrated to the West, knows what it feels like to be spoken down to by white people, to be told what her continent is "really like".
Adichie is especially brilliant at dissecting this latter form of condescension - both in writing and in conversation. Two years ago she enrolled to do an MA in African studies at Yale (an oddly humble choice given that she had just written a world-famous novel about the Biafran war). The experience was disappointing - "academia is not for me" - and she found many of the attitudes she encountered puzzling. She recalls a fellow student announcing: "The violence in Africa is different." "It's something I'll never forget," Adichie says. "This was someone who could end up formulating western policy towards Africa, working for the state department. He said 'You know, they're doing it with machetes.' And someone said: 'But there's violence in the inner city here.' And he said 'No, that's different, they're just shooting.' Adichie tells me the episode will feature in a future book.
Another condescending figure from Adichie's past makes it into "Jumping Monkey Hill", the most obviously autobiographical (and funniest) of the stories in The Thing Around Your Neck. The story is about an African writer's workshop that takes place in South Africa, presided over by a lecherous, arrogant Englishman called Edward Campbell. Campbell, "an old man in a summer hat", sees it as his right to tell the students exactly what kind of fiction they should be writing. A Zimbabwean is chastised for writing about a childless couple who visit a witchdoctor - this, Campbell says, is "terribly passé". He ticks off another student for featuring a gay character - "homosexual stories of this sort [aren't] reflective of Africa".
Adichie laughs when I mention the story, but when she wrote it, she says, she was motivated by rage. "I wasn't really attacking this man. For me the story is about the larger question of who determines what an African story is. You have this workshop of African writers, it's completely organised by the British, then this person who has his own ideas ... imposes them on these young, very impressionable people. I remember feeling helpless. You're sitting there thinking, this is the result of 200 years of history: we can sit here and be told what our story is."
Adichie says this with feeling, but there is nothing shrill about her tone. She has found a way of harnessing the anger she feels about all sorts of things - colonialism, patriarchy, Nigeria's history - and using it as inspiration for her fiction. In the process, she has achieved spectacular success in Britain, the country that used to rule her own. There are surely lessons in all this about the ironic inversions of post-colonialism. But if you attempted to spell them out, you rather suspect you'd end up in one of Adichie's stories.
