Love, hope, fear, power, chaos – the simplest words can have the deepest meanings.

To celebrate the 300th anniversary of St Paul’s Cathedral’s ‘topping off’, Britain’s bloggers were invited to say what they thought made life worth living. The stream of responses were projected onto the dome by artist Martin Firrell, making St Paul’s a literary beacon for London’s hopes, fears and values.

Firrell’s other projects have included projections onto the Tate Britain and the Houses of Parliament but this was the first time he let cameras in on his creative process.

Interested in the perplexity of the question and the range of responses, Firrell’s projections varied between the funny, the profound, the obvious and the politically challenging. Famous for themes of climate change, faith and cultural diversity, Firrell also projected his own ideas onto the walls of the Whispering Gallery and the cathedral’s West Front on Ludgate Hill, challenging, among other issues, the war in Iraq.

This documentary showcases the reaction of Londoners to such a thought-provoking installation. Interviewing writers and philosophers, it seeks to understand the significance of the responses in the 21st century. Above all, it reveals the power of art to engage with the public, transfixing people’s attention on the city skyline and forcing them to contemplate their own question mark inside.