When the sophomores came back to their rooms, they got a note saying "check your voice mail." However, their phones had been "stolen," so they had to check their voice mail from another phone.
The message was a mission assignment in the style of "Mission Impossible" that taunted them about being pranked by the SillyFroshForce and told them to go to a certain web page.
However, when they tried to go to the web page, they realized that they had no mouse balls. Those had been picked off too. So they had to find some other computer to use. Note that this prank pre-dates the commonality of optical mice and cell phones. A few victims did have optical mice, so we just stole those entirely.
The web page taunted the sophomores even more and told them to "Use the source." The smart ones realized that their next clue was hidden in the HTML source code of the web page.
The source code contained a Geography riddle, to which the answer was north. The clever sophomores realized that this meant that they had to travel to North Dorm (lounge) for their next clue.
Normally, the North Lounge is a relatively safe place. However, when herds of Easties trek into their lounge searching for a "clue" during the World Series, no one knew how they would react. The clue list was eventually moved outside the lounge to avoid incurring wrath of NorthDorm.
On the bulletin board at North was half of a Library call number. The other half, they were told, was under the piano in the Grace Hall lounge at Scripps. No problem, except they can't get into Scripps without a Scripps ID card, something that most Mudders don't possess.
Once they got the last half of their call number at Honnold, they were told to find that book, and their final clue would be near that book.
The final clue asked the sophomores what they were doing at Honnold, when their mouse ball was in their room, located _______ (ie: under sink, behind bookcase, etc). Once they retrieved their mouse ball, they would get their pillows and phones back.