The question of how labour and social movements interact with political parties (especially those claiming an ‘ally’ status, such Labour and Left parties) has long been preoccupying research and theoretical debate in the study of Contentious Politics. Yet, to this date, discussion has tended to focus on largely organisational issues (often with an intense tautological ring to them), eschewing the cardinal problem of policy content. This is quite unfortunate. For, in the abstract, party allies are obviously important for the future of any mobilisation; they are obviously both a source and an outcome of its particulars; and the politicization they perform obviously plays a decisive role in the way movements escalate or decline. The real question, which rarely gets explored, concerns the effect that concrete party policies (qua political strategies) have on movement fortunes – their dynamics and outcomes. Drawing material from the Greek experience of 2009-2016, this paper explores the dynamic relationship between movement-mobilisation and concrete party strategy. Ostensibly the by-product of movement anti-austerity mobilisation, SYRIZA (a self-proclaimed party of the ‘radical Left’) emerged as a key movement ally, and came to power in January 2015 promising an all-out clash with the neoliberal template, only to renege on its electoral pledge. During this time, its policy outlook changed (often dramatically) causing subsequent movement decline. In the process, SYRIZA was also thoroughly cartelised ‒ a process typically treated in the literature as a reflection of environmental influences ‒ without any serious attention paid to the role performed by party strategy. Aspiring to remedy this deficiency, the paper offers a thorough critique of the cartel party model and suggests remedies.