In a court room, "hanging judge" Apano hands down a harsh sentence. Outside in the streets, one man argues with a meter maid while another woman gets into a fight over parking with a short bald man. A non-human Link rides up to go after the short bald man, who hides. Once the Link leaves, the short bald man runs off leaking a pink gas… and everyone he passes start falling in love, kissing and hugging. The man passes by the courtroom and Apano starts releasing defendants.
The team gets word of the "man's" activities and it turns out he's a Link who was the basis for Cupid. They need to find the Cupid to secretly reverse the effects before a major criminal, Miguel Terrera, comes up for sentencing. The Cupid Link's trail leads to Denver so Nick and Kate are given the antidote and head out with Carl (who is immune). Jonathan tries to get a date with a lab technician, Marnie, without luck.
In Denver, they visit Carl's contact Richie, a gremlin that hangs out in a blue Mustang. He confirms the Cupid's ID as Ross Bowman and says he's hiding from a Link he disrespected, a Zaybar, who is a ruthless bounty hunter. The Zaybar wants Cupid who made his girlfriend… overly affectionate toward everyone.
Elsewhere in Denver, Bowman is meeting with his ex-psychiatrist who is desperate to get away from the obsessive Bowman. Nick and Kate arrive and take Bowman into custody, but the Link infects the psychiatrist and they get out just in time. Back in Chicago, Apano releases another prisoner as Page explains to the D.A., Williams, that they're working to get Apano "cured." While Nick and the others head to the rendezvous point, the Zaybar visits the psychiatrist and throw shim out a window, then gets the trail of the Cupid from his eye drops he left behind.
The hypochondriac Cupid continues to annoy everyone en route and a fight breaks out. The Cupid tries to escape without much luck and they continue. Back at HQ, Jonathan talks to Marnie about using a reverse-engineered antidote for a medical submission (and to get closer to her).
The team gets to the SU2 helicopter but the Cupid warns it can't handle heights. They continue but it turns out the Cupid's heart literally explodes when he gets too high so they're forced to land and continue by van, even though they're a thousand miles away. Page has to go to the D.A. and say there's a secret witness. She has no choice but to ask for an extension and Page suggests that she mention her dog died.
While the Zaybar gets ever closer, the Cupid warns he has to eat or he'll start giving off bile. Meanwhile Williams confirms the judge has given them another 12 hours. Kate takes her antidote redosage but before Nick can, the Zaybar attacks them, steals a car, and leaves with Cupid. Nick meanwhile is too busy falling in love with everything, including Carl and Kate.
They hit the road on the trail of the Zaybar and Carl quickly takes advantage of Nick's loving nature. Kate has to explain to Page by phone what's going on and the captain isn't happy. While the Zaybar continues to head for New York, even Carl begins to find Nick annoying. Back at HQ, Jonathan and Marnie are working on the reverse-engineered antidote but Marnie is still oblivious is to Jonathan's interest. Finally he suggests they test it on themselves and Marnie agrees in four hours.
Kate manages to intercept the Zaybar once they figure out its route and she ends up shooting the tires… but destroying the car when Nick jars her aim. The Zaybar is tough enough to withstand it and it hauls the dead Cupid out of the car then runs away.
Kate calls Jonathan to tell him to try and find a way to resurrect the Cupid. She's forced to explain to Page what happened. The captain is displeased. Jonathan suggests they get Cupid into a helicopter and fly it up so its heart expands and it revives. That works and the Cupid is back to normal, and they force it to cure Nick.
Terrera's trial continues the next morning and Judge Apano prepares to dismiss him. Nick and Kate arrive outside and have Cupid release its "antidote." The judge is back to normal and sentences Terrera to the maximum. Williams thanks Page although she's left to wonder exactly what he did. She's so intrigued she asks him for a date for dinner and Page agrees.
Later Nick forces Carl to give him all of his valuables back and he reluctantly admits to Kate that his being in love with life was like when he was in college. But he asks Kate to shoot him if it ever happens again, and says he never wants to be that happy again, and would rather be "happy" beating up on links. Meanwhile, Marnie and Jonathan test their "love potion" but nothing happens. Jonathan ends up asking Marnie out for dinner.