In this paper we trace the rapid growth and spectacular demise of online peer to peer lending in China. Drawing on a series of interviews conducted in China in 2017 and 2018, we follow the expansion of the sector from the establishment of the first major platform in 2007, through the introduction of limited regulation in 2015 in response to a series of platform failures to the final de facto closure of the whole sector by the regulator in 2019-20. However, contrary to claims that technology would reduce risk, the new platforms appear to have given rise to new risks by connecting dispersed borrowers and lenders whilst the regulator had decided to leave the sector to evolve without specific regulation. While there were hopes that P2P lending might increase flows of finance to the SMEs that are excluded from the formal banking system, ultimately too much of the activity on the P2P platforms was characterised by what we term 'transactional ambiguity' and 'legal fluidity': it occurred on the fringes of legality, often amounting to Ponzi schemes, fraud or unlicensed banking activity. In contrast to the banking sector, where their intermediation role ensures that banks are the focal point in the event of borrower default, and conventional moneylending, where moneylenders bear the risk of default, defaults and platform failures in the P2P sector distributed losses far and wide around the country, often to lenders who were not capable of bearing them. Whilst the central government did not formally stand behind the P2P sector (as it does with banks because of the systemic implications of their operations), the government could not help but become involved where P2P lending transmitted losses to lenders who were dispersed around the whole country. Ultimately, central government announced a wholesale reversal of policy that led to the sector effectively being closed down. The episode cautions against overly optimistic claims that technology can eradicate the risks of fraud and fundamental uncertainty inherent in lending, and reminds us that, without appropriate regulation and adequate internal controls, financial institutions will always operate in ways that result in instability.