The Best Laid Plans, a Contrabassoon and a Sinking Feeling

S4 E18: Darlene struggles to cope with the stress of construction; and after a serious accident, she reevaluates everything and makes a life-changing decision. Elsewhere, Lou, a familiar face from the past, returns as Mark’s combative contrabassoon teacher; but after he butts heads with Mark, Dan steps in, only to realize that their similarities may outweigh their differences.