In an attempt to cash in on some of the recent upswing in popularity of humorously inept teachers Jake swings by MUN and picks up some substitute teaching credentials. Almost as soon as he's certified as a sub hot lady teachers can't wait to be 'sick' to have a chance to call Jake at 6:00 AM and speak to him for a few minutes.
Almost as soon as Jake starts getting these 6:00 AM calls from frisky lady teachers he realizes that substitute teaching isn't for him. But because he cares about the children he can't quit in the middle of a massive flu epidemic - first he's got to get to the bottom of why there has suddenly been so much sickness among the lady teachers of St. John's.
By sending Tinny in to Holy Heart as an undercover student she is able to listen in on a few of the teachers talking about their feelings for Jake. Of course it isn't until Jake talks to Nikki and confirms that no one in St. John's actually has the flu that he starts to figure out what's been going on.
Mal and Rose knew the score all along but kept quiet because they liked seeing Jake woken up early by lady admirers.