James Bowen is a homeless man and former heroin addict, living on the streets of London down to his last bits of change. After a life threatening drug-related incident, his support worker Val, in an attempt to get him off the street, gets him into a council flat and prescribes him methadone. On his first night in his flat, James discovers a cat rifling through his food. Assuming the cat had escaped from somewhere, James tries to return the cat to his real owners. After letting him go, the same evening the cat returns to James's flat, this time with a purulent wound on his back leg. Worried, James consults his animal-loving but allergic neighbour, Betty. She informs James of a local charity vet where she volunteers, and names the cat Bob. Waiting on a queue at the vet, James misses a meeting with Val. After the appointment, James has Bob neutered and sets him free. However, Bob keeps following James into town, eventually drawing more crowds of people, making James more wealthy, and he eventually decides to keep Bob. Bob becomes a tourist hotspot, and James and Betty start to become romantically attached.