This essay examines the political and social significance of the intrusion of the supernatural into youth subcultures in two urban fantasy series: Cassandra Clare’s Mortal Instruments and Melissa Marr’s Wicked Lovely. Both series represent the idea of human youth mobility and social affiliation based on volition. The tolerant urban spaces through which their girl protagonists initially move accommodate a diversity of subcultural aesthetics. By contrast, the supernatural subcultures with which these girls become involved are fraught with conflict, and the mobility of their members is limited. Drawing on post-subcultural theory, we identify a tension between late modern and premodern social organization and political values in contemporary urban fantasy for young adults and compare how it is resolved in Clare’s and Marr’s texts.