How did Mr's frisby got captured?

Mrs. Frisby, the protagonist in "Mrs. Frisby and the Rats of NIMH" by Robert C. O'Brien, does not get captured herself. Instead, she seeks help from the highly intelligent rats of NIMH after her son, Timothy, falls ill. The tension arises when she navigates the dangers posed by a farmer's cat, which threatens her and her family while she tries to save Timothy and find a solution to their predicament.