Simplify the following text for a Grade 11 native English-speaking person.
Original: When Koror was down to six , Tom and Ian worried that they would fall against a possible immunity threat , Gregg , and his close ally Jenn , and started a plan with Caryn and Katie to vote out Gregg when they had the chance .
Simplified: When Koror was down to six , Tom and Ian worried that they would fall against a potential immunity threat , Gregg , and his close ally Jenn , and plotted with Caryn and Katie to vote out Gregg when they had the chance .