Strangers in the Night is a very short secondary quest available in The Witcher 3: Wild Hunt, taking place west of the Vegelbud Residence near the river, in Velen. The quest is initiated simply interacting with one of the three men camping by the river. After joining them there are a few dialogue options, leading up to Rufus, the Redanian soldier, accusing Manfred of being a spy for the Nilfgaardian Empire, believing him to be too well informed for his apparent guise as a merchant.
Geralt may choose to help either Rufus or Manfred, or alternatively to remain neutral. If Geralt helps one of the men, the other will become hostile and must be killed. The man Geralt aided will then give him a Diagram as a reward. If Geralt remained neutral, however, no reward is given after the men fight and the quest is completed.
If Geralt chooses to side with the Rufus, he will search Manfred's body and comment on his purse filled with Nilfgaardian Florens, suggesting that his suspicions were correct.