Two events 400 years apart, joined together by the thread of radical change. In 1517 Martin Luther overturned settled belief with his defiant '95 theses'. In 1917 the Bolsheviks stormed the capital to herald Communist conquest. RN revisits these two upheavals that have left deep and lasting legacies on the modern world, and ask—what do we know, what should we know, and what have we learnt?