Shawn's powers of observation work against him when he cannot help but reconcile his gorgeous Friday night date with her ex-boyfriend after solving the mystery of his series of white lies. Now alone in a bar, he spots Lassiter at a table, drinking heavily, marking a sad anniversary. Lassiter invites Shawn over and proceeds to pour his heart out, confessing that Shawn's skills astound him. While he doesn't believe he's psychic, Shawn somehow guarantees an arrest, whereas Lassiter, who used to be a great cop, now can't even solve the murder of a local astronomer. Everyone thinks Bryant Vallery died of natural causes, but the guy was relatively young and lived a healthy lifestyle. Lassiter tells Shawn that he knows there's more to it but can't prove it - then proceeds to pass out.
The next day, Lassiter can't remember any of the previous night's confessions, so Shawn decides, to boost his confidence, he'll secretly solve the Vallery case, feeding Lassiter information and giving him all the credit. He talks to the widow who tells him that Bryant and his partner Hugo, finally got the time they wanted on a large telescope. He started spending long nights at the observatory, soon after which he started feeling "off, " which was about six months ago. She also suspected that he was having an affair.
Shawn recruits Juliet into his plan, who will be covertly feeding Lassiter information. Back at the Psych office, Shawn tells Gus that their new case involves a dead astronomer at the observatory, which should make Gus happy, since Shawn knows that Gus goes to the Space Center every Thursday afternoon. Gus denies it, until he shows up at the Space Center to find Shawn now working undercover there as a full time employee.
It turns out, Gus hasn't been going to the Space Center for pure love of astronomy. He's interested in Jessica, a PHD candidate, who has been working at the space center to help pay for school. Gus tells Shawn he's been working a slow plan to ask her out, since she just broke up with a boyfriend. Shawn decides to speed things up, so he takes over the planetarium show so Gus can spend quality time with Jessica.
Shawn starts the show, then leaves to snoop around the observatory. He finds Hugo, and notices a page missing from the astronomer's logbook. Hugo tells Shawn that he's continuing their work alone for Bryant's sake. They spent 5 years just petitioning to use the scope, of which they only got 8 months of time on, which isn't a lot since it takes months to chart a finding in order to prove it's a discovery.
Shawn finds Gus, who finally got Jessica's phone number. Only problem is that Juliet checked Bryant's phone records and found the number of his lover. It's the same number. It seems Gus' crush has a motive, but Shawn's unconvinced. He wants to do more digging. The janitor at the Space Center tells them that Bryant had become a jerk, was applying for jobs way out of his league and, unbeknownst to Hugo, wanted to dissolve their partnership. Hugo, on the other hand, was always nice to everyone and even brought them all coffee everyday. Shawn and Gus check the logbook. They see that the astronomers took turns at watch and the page that is missing is the night of June 21st. Something must have happened then. On the way out, they see Hugo in the parking lot, bringing in the coffee and a suitcase full of his tracking printouts. Shawn tells Gus that Hugo brings them with him everywhere for some unknown reason, but what he does know for sure is that Hugo is not home.
Unable to break into Hugo's house, Shawn spots an odd purple flowered plant, that stands out from the rest of the garden. He takes it to Henry to figure out what it is. Shawn is thrown by the fact that Henry has a woman friend in his house and ends up dropping the plant on his porch and taking off.
Gus goes through with his date with Jessica to see what other information they can get and clear her as a suspect. She tells Gus Hugo is having a big press conference tomorrow. He and Bryant discovered an extra solar planet six months ago. Hugo must have finished tracking its orbit. This is an enormous discovery. Shawn, who has been tailing them, says they now have motive, telling Jessica she's no longer a suspect and ruining Gus' chances with her.
Shawn and Gus are at the press conference. Hugo says that the discovery was made on June 21st during his watch. In the middle of his speech, Henry calls Shawn and tells him that the plant he left on the porch was poisonous. Lassiter and Juliet arrive and Lassiter, who has been doing his own investigating steered secretly by Shawn and Juliet, says that Bryant was going to cut Hugo out of the discovery. Shawn hints at poison and Lassiter says none was found on the autopsy. With that, Shawn figures out that the poison would have to have been administered in small doses over time. Hugo must have put a little bit of it into Bryant's coffee every day over six months, killing him so slowly, no one realized it was happening.
With the case solved, Lassiter's got his confidence back, regardless of the fact that he knows he had some help, although he thinks it was coming solely from Juliet. And Shawn lets Lassiter know, that the head detective, in his own words..."astounds him."