The roundabout refers to "a roundabout at a road intersection, a circuitous route, a roundabout", using the preposition "in", see example sentence: This conclusion was reached in a roundabout but nevertheless perfectly reliable way. (from George Gamow's famous saying: "The conclusion was reached indirectly, but the way it was reached is quite reliable."), also: I heard the news in a roundabout way. I heard the news indirectly. .