In the automated Vauxhall Floating Gardens, high above the smoggy streets of London, Nightingale No. 48 is refusing to sing. Stern mechanic Shem Holloway brings in the Gardens’ brilliant but arrogant inventor, Lord Marchmont, to fix the broken automaton. But the clockwork nightingale has a secret, and soon both men find themselves questioning whether they should be trying to fix a mechanical heart at all.