Simplify the following text for a Grade 2 native English-speaking person.
Original: They discover Mr. Tumnus has been taken by the Witch 's secret police and meet Mr. and Mrs. Beaver who tell them about Aslan .
Simplified: They find out that Mr. Tumnus has already been taken by the Witch 's secret police , and meet Mr. and Mrs. Beaver , who tell them about Aslan .