Say the name Tony Krushner, and most will think of his award-winning epic, Angels in America. Yet this earlier and lesser-known work demonstrates Krushner’s politically urgent writing applied in an equally effective way.

A Bright Room Called Day follows a group of friends in 1930s Berlin, as political machinations and increasingly tangible danger causes fractures within their set. While the piece begins with a joyous and harmonious new year’s celebration, the jovial tone soon darkens as the extremity of the situation reveals rifts and tests loyalties. With the group’s left-wing politics, homosexuality and Jewish friends, the shadow of the Holocaust in the not-so-distant future haunts us from the start as the group optimistically predict short-lived power for Hitler and his Nazi party. The action is intercut with monologues from Zillah, a politically conscious and sparky young woman in the 1980s who sees similarities between president Ronald Reagan and the Fuhrer himself.

The core plot takes a look at a relatively unexplored (theatrically-speaking) aspect of the Nazis rise to power: the actions and fates of Communist Party supporters and members. While the ‘Reds’ haven’t exactly always found favour in the USA – and that’s putting it lightly – Krushner dramatises some of their struggles against the rise of Nazism, yet avoids a propaganda play by also highlighting the rifts between their supporters. Indeed, what is targeted more than any particular ideology is inertia – the failure to act at all. Politics aside, it’s also a powerful character-driven drama of human loyalties and where people turn when the darkest days arrive.

This revival by Secret Heart is presented by an impressive cast, in particular the five central figures, who perform effectively and fluidly as an ensemble; there is a great energy in the space when they are all working together, as they bounce off each other while also creating strong individual characters. Charlie Archer (Baz), Ethan Holmes (Husz), Laura Hanna (Paulinka) and Holly Morgan (Gotchling) all show nuance and passion as the tight-knit group react in differing ways to the oncoming storm of war, negotiating the script’s themes of fear, hypocrisy, action, inaction, disillusionment and responsibility with emotive and intelligent performances. Yet it is Alana Ramsey who may have the most difficult job, in portraying Agnes’s apparent fear, unwillingness or inability to commit fully to a cause. While the political loyalties and passions of her friends are perhaps easier for us to comprehend, Ramsey gives an excellent performance as a woman who is left floundering and uncertain in a turbulent age.

As Zillah, Charlotte Jacobs provides a sparky and confident contrast as her call to action takes her back to Berlin itself; her constant presence near or in Agnes’s apartment is particularly used to great effect when she, Ramsey and Elizabeth Andrewatha (as ‘Die Alte’) share the stage: one room, three very different women, all feeling the weight of a changing world.

The space at Southwark Playhouse’s ‘Little’ is used effectively, with Matt Haskins’s lighting design in particular impressing with subtle light and shade that doesn’t overpower. Director Seb Harcombe has created a piece that, at 150 minutes, maintains a healthy pace and keeps the audience gripped, even throughout the heavier sections of dialogue. While it is certainly worth reading the programme notes in advance, this production works both as an insight into a perhaps unknown aspect of a notorious period of history, and a broader, poignant look at idealism, self-interest and fear.

A Bright Room Called Day plays at the Southwark Playhouse until 16 August. For tickets and more information, visit the Southwark Playhouse website.