The Party starts at the end of a story that began in public school some 30 years previously, reaching its apex at the glittering 40th birthday party of powerful, popular Ben Fitzmaurice. The party provides a deft description of our greedy consumerist society through the alternative viewpoints of Martin, Ben's outsider school friend, and his seemingly mouse-like wife, Lucy.

No expenditure is spared for this celebration at the Fitzmaurices’ new acquisition, “The Priory”, whose remaining monks were evicted to make way for Ben and his wife, Serena. But the sweeping renovations are haunted – “the hallway strewn with Moroccan rugs occasionally parted to reveal a series of gravestones”.

Peopled with glittering celebrities as well as has-beens in denial, politicians on 5:2 diets, boy bands and comedians wearing kilts, the party is shadowed by silent waiters and security men all wearing black, quietly serving their masters.

This is a generously layered book and a dictionary definition which serves as an epigraph points out three possible meanings for the word “party”.

The first meaning is that of the celebration in progress; the second meaning of “party” in the political sense also fits this gathering where everyone is breathless with expectation, wondering if the prime minister, “Ed Buller” will attend. When he arrives, Martin describes him dispassionately: “His face, eggshell smooth, his hairline receding in the shape of an inverted three . . . his eyes too small for the rest of him, pressed into the doughy expanse of his features like pebbles in the face of a snowman.” But Martin’s cynicism is no match for the full blast of power – it is painful to read about Martin’s agonised sweating moments, fearing the humiliation of not being recognised as Buller approaches.

The publicity banner for The Party which reads "Are You Invited?" in yellow lettering has its finger on the double trigger; this is a book about us just as much as it is about them.

The Party takes its readers back to school with Martin, the scholarship boy who struggled to belong until he met charming Ben at public school. The insiders and outsiders, pettiness and bullying are familiar to anyone who went to any school but as Day reminds us, these particular bullies are set to become leaders of government – not only clever Ben but also stupid obnoxious Jarvis who haunts Martin like a "smear".

The third and final dictionary meaning is “the idea of a person or people forming one side of a dispute as in the guilty party” and the book opens in a police station where Martin is being questioned. We don’t know why, and won’t find out until the end of the novel, yet the pace never flags.

The powerful will protect each other at all costs and Martin and Lucy are dispensable. As underdogs, they have suffered condescension as well as considerable financial benefits from their years of friendship with the Fitzmaurices.

Martin and Lucy are in denial of various aspects of their lives but their insight and characters grow considerably as The Party progresses. Martin is in denial about the truth of his relationship with Ben yet there is plenty for the readers to infer about Ben between the lines of his narrative, especially when juxtaposed alongside Lucy's. One of the funniest and saddest differences in their separate accounts of Ben involves a pair of very expensive trainers with striking pink soles.

There are many unlikable aspects to Martin – his cowardice and blind adoration of Ben, his snobbery and cynicism – yet I was surprised to find how much my sympathy for him increased as the story progressed. I wondered if Martin was benefitting from the presence of Lucy, who is the true hero of the book.

In a novel that is full of surprises, Lucy is the most surprising of all and she is no mouse. Complex, intelligent and funny, her heartbreaking love for Martin is the golden light that spreads through these pages turning a dark brittle satire into a moving and rich exploration of the human condition.

• Martina Evans is a poet and novelist. Her latest collection is The Windows of Graceland, New and Selected Poems published by Carcanet