Helen Sinclair doesn't know what hit her. One moment she was trapped in a dead-end job in 1960s London, and now she is transported back to Renaissance Italy over three centuries before. Florence is a city in turmoil. A new plague stalks the streets. A ferocious behemoth rampages through the vineyards. And Galileo Galilei, celebrated scientist, astronomer and old friend of the Doctor, is imprisoned in his own villa for heresy.

But why has Galileo summoned the Doctor? Who are the mysterious Fortuna and Cleaver? Why have they been sent to Earth? And what is Galileo's secret? Is it the last thing he saw before he went blind?