a friend in court字面意思是法庭上的朋友，引申为有势力的朋友。

【例句】
He was bloody safe he wasn t run in himself under the act that time as a rogue and vagabond only he had a friend in court.
那回根据法令，他差点儿就作为无赖或流浪汉被关进去，亏了他有个有势力的朋友，这才得以幸免。

A friend in court is better than a penny in purse. 
朝中有友，胜如囊中有钱。