As Dr. Mike's birthday approaches, the kids decide to do something about her unmarried status

Dr. Quinn's mother in Boston is ill. Dr. Quinn takes the children to Boston.

Dr. Quinn has met a very nice doctor in Boston and is conflicted about staying.

Dr. Mike and Sully go to Rev Johnson for a honest discussion regarding their upcoming marriage.After originally agreeing they have no conflicts, the couple begin reliving their past difficulties via prior show clips since they first met.

The town of Colorado Springs is preparing for an event of a lifetime, the marriage of Sully and Dr. Mike. Unexpected guests include Dr. Mike's mother Elizabeth Quinn and two of her sisters Rebecca and Marjorie. They have brought with them enough Boston finery to pull off a splendid society wedding. Meanwhile General Custer has put out a bounty on Cloud Dancing which could interfere with the wedding.

Bolstered by the long-awaited arrival of the railroad, the citizens of Colorado Springs busily prepare for the biggest social event in the town's history, the wedding of Dr. Mike and Sully. The first train carries some surprise visitors, Dr. Mike's mother, Elizabeth, and sisters Marjorie and Rebecca, who have unexpectedly traveled all the way from Boston for the occasion. However, their elaborate wedding plans threaten to ride roughshod over the townsfolk's more homespun arrangements. Sully, meanwhile, is crestfallen to learn that Gen. Custer has placed a bounty on the head of his close friend Cloud Dancing, who he had planned to have as his Best Man.

Dr. Mike's mother and two of her sisters arrive with a young Dr. Cook to deliver the baby. Conflict arises between Horace and Myra which ruins Preston's hotel groundbreaking. Sully works to prevent Cloud Dancing's transfer to another reservation.

Dr. Mike leaves in the night to treat Sully, who was wounded by sergeant O'Connor while helping Cloud Dancing. She goes into labor with only Sully to assist her.

Michaela gets a surprise visit from her sister Marjorie, who turns the town upside down with her radical ideas. But even though Michaela partly agrees with Marjorie, she has to ask her to start thinking about other people's feelings.

Marjorie, Dr. Mike's sister returns to town as a member of the Women's Temperance League to try to outlaw alcohol. Jake starts believing that there may be something going on between Hank & Ms. Teresa. Meanwhile Grace has turned to drinking to help comfort the recent death of her adoptive son Anthony.

Dr. Mike's mother and oldest sister visit for thanksgiving just as an outbreak of diphtheria hits Colorado Springs.

Dr. Mike struggles to control the diphtheria outbreak and disagrees with Andrew on whether to use a new treatment.

Michaela and Sully reminisce about the ups and downs of their relationship and make a momentous decision about their future. While returning from a week long trip with Sully, Michaela stumbles and falls, sustaining a head injury. The couple takes refuge in an abandoned cabin where Sully must keep Michaela awake to prevent her from slipping into a coma. Together, they reminisce about the myriad different experiences -- good and bad -- they've shared together and then make a pivotal decision about their future.