Deep below the streets of London, descending past Temple tube in the beating heart of the city, lies a dark secret. An illegal clinic has been set up in an abandoned subterranean network of tunnels. Daniel (Mark Strong) is a surgeon driven by personal tragedy to treat anyone who is willing to pay for medical help outside the system. Aided by Lee (Daniel Mays), a disgruntled transport employee, and Anna (Carice Van Houten) a guilt-ridden medical researcher, they treat a variety of increasingly desperate and highly dangerous patients, as Daniel's morality is tested to the limit.