Mark is home sick but is eager to get back to school. Willie tells Val he is feeling sick but she thinks he's faking to get out of a school project. The school calls and it turns out Willie was telling the truth. Finally, Valerie herself falls ill and the boys don't make her feel any better by totally destroying the kitchen.
This is an average episode with an unoriginal plot. They should have dealt with Val's guilt about not believing Willie, but instead they use tired tropes such as the "sick-person-with-a-bell-drives-caregiver-crazy" and sight gags like a dirty, run-down house (Val's slippers stick to the kitchen floor).
You can skip this one without missing much. I wasn't impressed.