We flashback to 1990 SBPD. Herb Wilkins, the Chief of Police at the time, is giving then-detective Henry Spencer a lecture on his mistake on a case. Herb ends up taking Henry off the case and replaces him with SBPD's star detective team, Peters and Boone.
We then flash forward to present day, where we immediately discover that the former Chief of Police, Herb Wilkins, has been murdered - execution style. Shawn and Gus show up on the scene and Henry explains the situation. Seconds later, Peters and Boone arrive on the scene. Shawn immediately doubts their ability - claiming they are too old to solve the case. Henry, however, vouches for them, saying they were the best of the best back in the day. While standing over the body of Herb, Shawn has a vision and is about to share it with the group, but Peters and Boone step in and say it first. They saw the same clue Shawn did. The gun found on Herb didn't belong to him. Peters and Boone show the group that the serial number on the gun had been filed off. Shawn and Gus are shocked to see that Peters and Boone are well on their way to beating them at their own game.
Back at SBPD, Peters and Boone have been brought on as consultants on the murder case. Shawn and Gus are there trying to make themselves useful; however, Peters and Boone want nothing to do with Shawn and Gus. They see them as measly "palm readers" with fake titles and no experience. Shawn and Gus decide to take matters into their own hands and find a lead of their own. They head to Herb's bait and tackle shop down by the docks. They question a worker - she lets them know that Herb was seeing a young girl with red hair - the same girl who worked at the shop across from Herb's called "Pacific Treasures" but hasn't been there in two days. At that point, Peters, Boone, Shawn and Gus are faced with each other, and are forced to share knowledge about the case. It is then that they get a call from Juliet with the OK to search Herb's house.
Shawn and Gus arrive at Herb's house thinking they are the first to get there. But they soon realize that Peters and Boone got there long before them, and are already deep into their investigation. But Shawn gets a vision - a clue telling him that someone came to Herb's house before them looking for something Herb was hiding. Peters and Boone immediately defend Herb to Shawn and Gus, saying he would never get mixed up with anything shady. But Peters and Boone take the clue seriously, and Shawn and Gus overhear Peters and Boone determining that if Herb was hiding anything it would be in his locker.
They arrive at Herb's locker at the local public swimming pool. Shawn determines that Herb's locker number is #22 - not locker #9 as Peters and Boone thought it was. Shawn determines this after seeing a 'Shawn Vision' of a bunch of lottery tickets in Herb's home with the #22 on every single one. They break open the locker, and to each of their surprise, find drugs in a black bag.
Back at SBPD, they find out that Herb withdrew 50 thousand dollars before he was murdered - which doesn't bode well for him considering a bag of drugs was just found in his locker. Peters and Boone take off, and Shawn and Gus realize that they swiped a book of matches from the evidence lot. As a result, Shawn and Gus decide to tail Peters and Boone. When the two teams converge, Shawn and Gus convince Peters and Boone to let them in on the clue they stole from evidence. Peters and Boone show them the evidence: a book of matches that says, "The Dollhouse" - a hot, local nightclub.
Later, at the club, they find out that Herb had been there many times to visit one of the nightclub's employees, Saralyn - who's known in the club for liking to hustle cash. Just then, they get a call from Juliet telling them that a man named Otto, a man involved in drug deals, owns The Dollhouse. Juliet realizes they are already at the nightclub and warns them not to mess with Otto. Naturally, the four don't listen and break into Otto's office. They find a gun with a serial number scratched off of it - just like the one they found on the scene of Herb's murder. They also find the same type of black bag that was in Herb's locker. Just then, they spot Otto and his men. They get involved in a chase. The four narrowly escape, only to rush out of the club to find that Otto has been shot and killed.
Back at SBPD, the four are in trouble for going to "The Dollhouse" before the police, and are especially in trouble for possibly propelling the murder of the department's only suspect. Chief Vick wants to know what they found in Otto's office, but the four do not reveal anything. As a result, Vick fires them off the case. But Gus and Shawn realize that Peters and Boone were not letting Chief Vick know exactly what they found in Otto's office - that in fact, Peters and Boone did take a piece of evidence from Otto's office - a booklet containing a stack of Dollhouse job applications. From this new piece of evidence, Shawn discovers that Saralyn put Herb as her emergency contact on her job application. This intrigues the four guys and they decide to rejoin the case despite Vick's order to stay away.
They head to Saralyn's house. They are greeted by a young woman who is not Saralyn. The woman lets them in the house, and they immediately ask her about Saralyn's involvement. The woman lets the four know that when she worked for Otto at The Dollhouse, he had her do "drops" at a place called "Pacific Treasures" to make extra cash on the side. She explains that the only way out of the job was to pass the job along to someone new - that new person happened to be Saralyn. Shawn puts two clues together, and lets the group know that Saralyn was seen "working" at Pacific Treasures - a place directly across the way from Herb's bait and tackle shop. Shawn remembers from Herb's house a picture of Herb and another young girl, his daughter, who looks exactly like Saralyn does. And because he saw Saralyn as his own daughter practically, Herb was trying to protect Saralyn from Otto and the drug lords - which explains the bag of drugs in the locker, and why he withdrew 50 thousand dollars from his bank account. He was trying to buy Saralyn's freedom. Shawn, Gus, Peters, and Boone find Saralyn at Herb's house and try to convince her that she needs help. But Saralyn tells them to go away because everyone who has helped her in the past has been killed. After Saralyn turns the four away, we see that she is not alone in the house - a man is there with a gun pointed at her head. The man is Randy - the drug lord who hired Otto who hired Saralyn. In an attempt to save her, the four try a Peters and Boone technique called the "Bark n Mark". Shawn and Gus make a distraction by barking like dogs, while the other two save the girl. The Bark n Mark works, and Lassiter and Juliet are able to take down Herb's murderer and save Saralyn.
In the end, Peters, Boone, Shawn, and Gus discover a mutual respect for each other and each of their unconventional detective styles, despite their initial perception.
Sildenafil citrate is a drug sold under various copyright names including Viagra as a treatment for erectile dysfunction. Here it is combined with the image of Niagara Falls, although it may also in the title suggest the droop for which Viagra is used.