A rogue black hole emerges out of nowhere, swallows the planets one by one, and then stretches the Sun out into a long stream of glowing dust. Over the following months it faded – but when astronomers traced back the event, the conclusion that best fitted was a deadly encounter with a wandering supermassive black hole. Should a third black hole get involved – perhaps because one of the colliding galaxies already hosts a spiralling pair – then one of the black holes can be ejected. Either way, the result is a wandering supermassive black hole. Others will be signatures of a violent encounter between a star and a wandering black hole.