CSI: NY

A naked man covered in blood runs through the streets of New York, wearing only strange-looking devices on his head and arms. He stumbles inside the precinct, surprising everyone, including Mac Taylor and Don Flack. As crumbles on the floor, he shouts "I killed him!"

The man tells Mac the name – Kevin Murray – and the address of his victim, and the exact time when the crime happened: 11:45. "It's 10:15", Flack says. Mac asks the man when it was, that morning, the previous night? The stranger whispers something in Mac's ear and dies.

In the precinct, Mac and Hawkes start processing the dead man, looking for clues of who he is. Flack finds Kevin Murray at home, taking a shower, and takes him to the precinct. Kevin claims he's never seen the dead man, who obviously didn't kill him. "It's a little early to tell", Mac explains. "He said he came from the future, and he doesn't kill you until tomorrow."

As Mac and Hawkes follow the bloody footsteps on the street, a man from the crowd confronts them, demanding punishment for the naked man. The CSIs find a hopscotch course drawn on the sidewalk, and collect pieces of bloody chalk, and a bloody glass fragment that might have been the murder weapon.

In an interrogation room, Kevin tells Flack he's a Physics major, and insists he doesn't know the dead man. But he seems interested in what he'd have to say about killing him, including the coming from the future part – which Mac refuses to discuss, since it's part of the investigation.

In another part of the town, Stella and Danny have to deal with a young woman who died in a deli, while eating a pickle. She has an allergy inhaler in her purse, but no ID. There are signs that there was someone sitting with her. Her toes and fingers show signs of cadaveric spasm. Witnesses tell Detective Angell what happened: the young woman started acting as if she was having an orgasm, much like Meg Ryan in When Harry met Sally, but pleasure turned into pain until she collapsed. A guy had come in after her, sat with her then left; he wore a Chelsea university T-shirt and had a T-Rex tattoo on his forearm.

In the morgue, Sid analyses the naked man's body, with some bizarre results. He had some kind of chip implanted in his hand – self-implanted, by the look of it. Also, he's got a needle lodged in his brain.

Stella receives a present from Drew: a parachute and sky diving lessons. She tells Mac about his advances, and that he's too aggressive for her. Mac notes she was smiling when she opened the box, and advises her not to worry so much about the risks, and enjoy what that romance might bring her, as he learned to do with Peyton.

Adam finds out the chip is a RFID (radio frequency identification) transponder, and it's active: receiving and transmitting a signal to distant control point. Following the coordinates it is transmitting to, they find what seems like a laboratory – with a very elaborate attempt at a time machine. There, Hawkes recognizes the John Doe as Dr. Martin Browning, a respected scientist considered a genius in his field. "There's a fine line between genius and insanity", Mac remarks.

In the trash, they find signs that the victim might be out of money: he was trying his luck at the lottery and horse racing. But Browning had received a large money prize for his science achievements, so the evidence seems to be pointing at someone else – who might know or even be the killer.

Back at the morgue, Sid shows Danny and Stella the dead coed had 27 sad faces drawn on her body. Weirder still, she died of aortic aneurism, due to extreme sexual excitement. She also had a strange drug in her system, which might have caused her death.

Adam shows Lindsay Dr. Browning had posted an ad online looking for an assistant for his time travel experiment. The needle in Browning's head was probably there since infancy, and Sid suggests to Mac and Hawkes it was probably causing him to have seizures. He'd had no memory of having a seizure afterward, and they theorize he might thought he'd been to the future after each of these blanks. The needle, by the way, was connecting the two hemispheres in his brain, linking the logic area to the intuition and possibly causing him to be a genius in the first place.

Since Browning had an honorary position at Chelsea University, where Kevin Murray studies, Hawkes goes talk to the Dean. The Dean expresses his admiration for Browning, but also his despise for the idea of his research in time travel. Hawkes notices the Dean has a large bruise on his forehead, and there was blood on the door knob at Browning's apartment. The Dean admits to trying one more time to convince Browning to get help, but tells Hawkes he was attacked by someone who said he was Browning's assistant.

Stella analyses the coed's belongings and finds out her allergy inhaler had been tampered with. Someone switched the medicine inside it, and left a print. Danny finds the dust on the other person's seat seems connected to an elephant.

As a parade goes down the street, a dead body falls from above. It's Kevin Murray, and he's right on schedule. He was electrocuted and thrown through Browning's window. It seems he broke in, since the place was still sealed up for investigation. They theorize Kevin was the mysterious assistant. Mac remarks that the wiring was faulty. They find a manual on the time traveling machine that was not there the first time, and it has blood drops on its cover.

Stella tells Danny the drug inside the inhaler is a sexual enhancer, currently being tested on campus students. The patient files may tell them who gave her the drug. Danny tells Stella the dust he collected was not linked to an elephant, but to a 4 million-year-old mastodon. This leads Danny and Angell to Brent Vandeman, a student who works with mastodon bones at the museum – and has a T-Rex tattoo. He tells them the girl's name was Robin Graham, and he also tells about a college party with a raffle, and how he won Robin for the night. She freaked out and left, so he followed her to the deli. He was trying to talk to her when she started moaning, then he ran. Stella and Angell question the control patients for the study and find nothing, until Angell remembers the health center has their prints on file.

Lindsay shows Mac the pictures they took of the hopscotch are actually showing calculations related to Browning experiences –using game theory. Browning knew the machine was broken and tried to calculate Kevin's choices of survival if using it. Hawkes brings the information that Kevin's body showed signs of defensive wounds. There's a fingerprint on the cover of the manual that doesn't belong to Kevin, and the blood on it not only matches Browning's, but was wet – which is impossible, since he was already dead. Mac proves the blood was rehydrated, which indicates there was somebody else in the room: the real killer. From three partial prints, Mac and Lindsay reconstruct one thumbprint. That leads them to Leo Tyler.

Leo Tyler comes to interrogation sporting a big black eye, and we learn he was just saved from a beating by the arrival of the police. Tyler owes money to bookmakers. He tells Mac he tried to apply for the assistant position, but Kevin was already hired. But Tyler stayed around, and actually believed Browning was traveling in time. He started using it to win money, but Browning refused to help him. Tyler was the one who hit Browning with a glass orb, thus inflicting the fatal wound. Browning escaped him and ran naked to the street. Tyler tried to run after him, but he was too late – and then we learn he was the one outside the precinct demanding to know what was going to happen to the naked man. Tyler forced Kevin to operate the time machine, believing he'd bring an answer to his gambling problems. Then Kevin was electrocuted.

The print in the inhaler leads Stella and Danny to Kelsey Coulter, who tells them Robin was trying to join a sorority. During an initiation ceremony, the others draw the sad faces on her, and decided to "help" her get rid of her virginity. Kelsey thought it would be a good idea to substitute the sexual enhancement drug for Robin's allergy medicine, to make her loosen up, and she provided the flowers that would make Robin need the allergy inhaler. She didn't count on the fact that, once the allergy medicine didn't work, Robin would keep using the inhaler, trying to find relief – and instead getting a too high dosage of the sexual enhancement drug.

With the cases closes, Mac's in his office, checking his mail, and he receives a letter from Peyton. It's the end for them. A heartbroken Mac finishes the night playing his bass with his band. Stella, who had found the letter in his office, goes there to watch the show and be there for him.