It may be low-budget, but And While London Burns has the grandest set in operatic history: the City of London itself.

In truth "opera" is hardly the word. It's closer to melodrama as Mozart would have understood it: spoken drama (libretto by John Jordan and James Marriott) interwoven with music (by Isa Suarez).

Mozart, though, would not have understood the form which the 70-minute performance takes. You download it to an MP3 player, then listen while walking through the locations it describes. The download is free, although one location requires an entry fee of £2.

The aim is to disentangle what the libretto calls the "carbon web", the network of wealth and exploitation, often London-based, which strangles the planet by fuelling our oil addiction.

A murder story, then, but from the start it's plain whodunnit: oil companies. Some will find it tendentious; others (count me in) will have their darkest fears confirmed. As the narrator (Douglas Hodge) describes London's globally warmed fate, you almost feel the Thames rushing to engulf you.

It is not opera as we know it, but an ingenious way of reanimating this monstrous city, showing some of what lurks in its shadows.

• www.andwhilelondonburns.com