This article argues that contemporary urban crises demand a radical rethinking of planning history, yet these crises simultaneously constrain the capacity for radical imagination, a tension conceptualized here as the radical catch. Urban planning and history have historically served as instruments of statecraft and capitalist development, contributing to the very crises they now confront. This article reframes radical planning history not merely as documentation of subversive practices but as a historiographical project aimed at transforming the epistemic foundations of how planning’s past is known and narrated. It first defines radical planning history and its urgency, exposing the ideological and institutional roots of urban crises. Historicizing the Crisis interrogates planning’s presumed neutrality and foregrounds its role as a modality of power. An Alternative to Crisis recovers forgotten planning practices and utopian visions to unlock imagination and challenge closed epistemologies. An Alternative to Crisis Determinism critiques linear historical causality, emphasizing the contingent and reversible nature of urban development. Through these three movements, critique, recovery, and epistemic re-foundation, the article positions radical historiography as a method for converting crisis from obstacle to opportunity, offering frameworks for more just, inclusive, and resilient urban futures.