Two single and extremely eccentric New Yorkers are subject to constant interference from their equally eccentric friends when they begin dating.
Nate is set up to go on a blind date with Susan, only when he goes to pick her up, he picks up Marni, who was set to go on a different blind date. After talking through dinner, they realize they are perfect for each other, but also realize that they are on the wrong dates.
To make it up to Marni for throwing Todd out on their first date, Nate decides he will spend a day hanging out with Todd. However, Nate doesn't really want to hang out with him. Nate makes up excuses to avoid Todd, but Marni ruins his plans. Todd joins in on a basketball game that Nate and Bowie are playing. Todd continuously harasses Nate, causing Nate to bring out his true feelings about Todd.
Marni has never seen Nate's apartment, so she invites herself over one night. However, Nate is embarrased to have Marni see the clutter in his apartment, so he makes excuses to keep her away. Tess tells Marni to break in to see it while Nate is at work, only they get more than they bargained for when they do.
Nate decides that he wants to become closer to Marni, so he brings a cup of her favourite tea to the hospital where she works. When he gets there he is surprised to find that Marni has another boyfriend, albeit an imaginary one.
Nate spends the night at Marni's for the first time, and they decide to have a picnic the next day. The only trouble is Marni's father, who abandoned her, causes some problems on the way to their picnic.
On the night before, Marni informs Nate that the next day is her birthday. Nate goes out scrambling for the perfect gift, but is always outdone by Todd. When Nate finally has the perfect gift, he can not give it to Marni because they keep getting interrupted. But when he finally does, it brings the two closer together.
Marni is up for a promotion at work, but when she doesn't get the job, she falls into a depression. Nate tries everything he can think of to snap her out of it, including seeing what he thinks is a therapist for advice.
Marni and Nate have a really bad day, so they decide to lock themselves inside Marni's apartment to disconnect from the world. Only it is difficult to stay disconnected for Marni when it starts snowing.
Nate takes Marni to meet his mother, who is residing in an asylum. The only problem is his mother doesn't like Marni, and Marni is desperate for her approval.
Nate faces his fears when he attends the funeral of Fred the Statue Guy, but accidentally takes communion even though he is Jewish. Elsewhere, Marni introduces Tess to her hairstylist, who when washing Marni's hair, causes Marni to have ""hairgasms"".
Nate loses a bet to Bowie, and must buy him a $29 hamburger. Just as they are about to leave, they run into Marni, who invites herself out with them. Nate needs to go get cash from the ATM, only he runs into trouble with a homeless man he tries to help. All of this delays Bowie from his hamburger, which he fasted for 24 hours to have.
Todd, in an attempt to break up Nate & Marni, sets Nate up by getting him drunk, and placing him in bed with the person he has a lot in common with.
Nate wakes up in Natalie's bed, and quickly gets out of there. He later tells Marni, and about a kiss shared between Nate & Natalie. Marni decides she needs to kiss a guy to be even, which leads to Nate and Marni "breaking up". However, Marni is reluctant to give up, and chases Nate down, who says his speech was only to say he is sick of Marni's behavior, and that they will be together forever.
