If first impressions count, then the political force that wants to transform Spain in 2015 consists mainly of student types and self-conscious outsiders. That, at any rate, is the scene when you enter Podemos’s crammed, disorderly office in Madrid’s popular Lavapiés district. Posters are being prepared for the movement’s first big street demonstration, planned for 31 January. A young woman sitting in front of a computer says she has no job and decided to become a Podemos volunteer because “if we don’t start taking things into our hands, la casta will just continue as before”.

This is the closest thing Spain has to Syriza, the radical leftwing party that just came to power in Greece. Only a year after its launch last January, Podemos (“We can”) is riding high in opinion polls. General elections are due at the end of the year. Just like Syriza, Podemos has a charismatic leader, the pony-tailed 36-year-old professor of political science, Pablo Iglesias. Like Syriza, Podemos calls for an end to traditional politics and rolling back austerity. Its key target is la casta (“the caste”), the dominant two-party system that has ruled Spain since democracy was restored in the late 1970s, after Franco’s death.

Opposite the Podemos office, there’s a book shop run by some of its activists. Browsing through it feels like you’ve stepped into a time-machine: there are collections of Lenin’s works, and books on the Italian communist thinker Antonio Gramsci and the French 19th-century revolutionary Louise Michel.

The more likely clue to Podemos’s rise can be found on the television news: an endless stream of revelations about corruption cases. Spain’s macroeconomic situation may have improved, but that hasn’t translated yet into improved living standards: youth unemployment still stands at a staggering 50%. Podemos taps into the despair over these numbers just as Syriza has done in Greece. It offers new young faces and resorts to social media in its bid to modernise Spanish politics, calling for more social justice and democratic accountability of the elites. But beyond that, its programme remains vague.

Podemos certainly fascinates. Unlike Syriza, it didn’t even exist a few years ago. It stormed Spanish politics last May by gaining an unexpected 8% of votes in the European parliamentary elections. This came as a surprise to many. In fact it was the result of a clever strategy put together by a small group of Madrid leftwing intellectuals.

This is how it happened: when the 2011 Indignados youth protests died down in Spain, a group of political scientists from the capital’s Complutense university, including Iglesias, saw an opportunity. They built on the online networks for the Indignados and put into practice some of the political techniques they had learned while studying Gramsci and the Argentinian post-Marxist political theorist Ernesto Laclau, an influential advocate of political populism. Out of this was borne Podemos’s central narrative: “The people versus la casta.” “They understood the key was not to dwell on class consciousness,” says political analyst Fernando Vallespín, “but to frame the very perception of politics.” It worked. Many Spaniards watching the eloquent Iglesias on TV or online started to identify the “casta”, the ruling class, as the source of their woes. One only needs to remember past headlines about Spain’s spectacular economic success story in the early 2000s, when easy credit fed a construction bubble, to realise how much of a boom-to-bust phenomenon has weighed on the national psyche. One middle-aged Spaniard put if to me this way: “We discovered we weren’t as good as we thought. We thought Spain had qualified to be at the heart of Europe, and all of a sudden, we were rejected to its lame periphery …”

There is an admirable romanticism to Podemos shaking up a sclerotic political scene. But behind its utopian energy there is more cold-blooded realpolitik than meets the eye. Podemos portrays itself as giving a voice to the ordinary citizens consulted on the internet or through hundreds of spontaneous assemblies called “circles”. Yet once the online voting has happened, the overall message is decided by a 10-member coordination council, nominated by Iglesias. At its worst, Podemos could resemble something like Leninist-centralism-meets-the-digital-era.

Explaining his communication strategy, Iglesias once pointed out how in 1917 Lenin “didn’t talk to the Russians about ‘dialectical materialism’, he talked to them about ‘bread and peace’”. The Podemos leader also believes that “Heaven is not taken by consensus, it is taken by assault.” Such statements have made it easy for critics to accuse Iglesias of authoritarian tendencies, influenced by outdated ideologies.

Iglesias and his close circle of friends in the Podemos leadership have spent time in Venezuela and Bolivia in the last decade, some of them acting as advisers to regimes whose democratic credentials aren’t exactly solid. Questions have been raised in the Spanish media about financial dealings from the regime of the late Venezuelan leader Hugo Chávez, whom Iglesias has expressed admiration for. Podemos has since toned down its rhetoric about Bolivarian revolutions; it now claims to want to mimic northern European social democrats instead.

But the impression of ideological muddle endures. During the Maidan protests in Ukraine, Iglesias largely came down on the side of Putin’s propaganda. And when Syriza formed a coalition with the antisemitic, far-right Independent Greek party, Iglesias defended it as “a programmatic choice”.

Podemos has successfully captured a mood of popular protest in Spain, but it is now aiming to structure itself as a credible and reassuring political party. It claims to renew democracy, yet it knows complex issues cannot always be addressed via online petitions. It has the ambition of a mass movement but is run by a tight circle of professors. It talks about hope but its casta narrative is very Manichean.

Some say the pragmatic transformation is already under way. They compare Pablo Iglesias to the young Felipe González, the former socialist prime minister who understood that his party needed to shed itself of radicalism in order to be elected in 1982. Spain, like Greece, is undergoing a generational shift. Diego Pacheco, a Podemos activist born in 1986 – the year Spain joined the European Community – speaks passionately about a quest for “empowerment”. “Podemos is not about being anti-EU, but about finding a way to move beyond the system that emerged from the post-Franco transition that our parents were part of,” he says.

Spain’s economic recovery will make it harder for Podemos than Syriza to win elections. Its main competitor, the Spanish Socialist party, still has more strength than Pasok. The digital meeting place Podemos has built might also show its limits. After Greece, Spain is likely to be the next country entering uncharted political waters in 2015, but it would be naive to think the electoral outcome will be as clear cut.