Really, even though Seohyun is dubbed 'The Innocent Maknae', did they really know the truth?

Here's the story. Basically, one day... Kyuhyun said he was going to visit a friend's house. The Super Junior members are fine with that. Right after Kyuhyun leaves, they suddenly get a call from Girls' Generation saying that Seohyun has gone out somewhere without telling them. This has never happened. Puzzled, they meet up at a hotel and try to piece it together. Where did Seohyun go? More than that, why did both Kyuhyun and Seohyun go at about the same time...?