Total opposites, always together and both unlucky in love.
Cath is scatty, messy and emotionally closed, and Si is impossibly tidy, bitchy and desperate for a man of his own.
They live near each other in West Hampstead, close to their other best friends Josh and Lucy - who are married, with a devil-spawn child called Max and a terrifying Swedish nanny, Ingrid.

When Portia steps back into their lives - beautiful Portia, the undisputed queen of their group at university, who broke their collective hearts one night and from whom they have all gradually, silently, grown apart - her reappearance sets off a chain of events that tests Cath and her friends to the limit.
Does Portia have a hidden agenda, or is she just looking for happy endings all round? Whatever the answers, none of them could ever predict the outcome ...