The following contains major spoilers from CSI: Vegas Season 3, Episode 9, "Heavy Metal," which debuted Sunday, May 12 on CBS.

With CSI: Vegas two episodes away from its series finale, the CBS show finally delivers the hard-hitting reveal that audiences have been waiting for ever since Season 3's Big Bad was introduced. "Heavy Metal" clearly confirms the team's -- and the viewers' -- suspicions about who's behind the robot murder, but to get there, the episode goes through yet another case of the week that's more quirky than it is tense or memorable.

"Heavy Metal" is a spotlight episode for Sarah Gilman's character Penny Gill, who's working toward becoming a CSI Level II. It brings back Penny's surprise engagement to assistant medical examiner Jack Nikolayevich, and also gives a little bit more screen time to Jay Lee as Chris Park, since he's supposed to be Penny's partner. And while the case is a bit better developed than some other Season 3 episodes, Penny isn't a strong enough character to carry the entire hour.

CSI: Vegas Sets up Its Final Showdown

Audiences Now Know Who Season 3's Major Villain Is

The biggest development in "Heavy Metal" is what happens in the final few minutes. Dr. Maxine Roby is finally able to get some more evidence against technology entrepreneur Truman Thomas, and a very brief non-interview leads her to discover tellurium dust on his shoes that eventually points the team to a tellurium mine owned by Thomas. Inside the mine is another robot and all the proof that Max needs to put away her new nemesis. But being that the bad guy is tech-savvy, it's far too easy to get into the mine and impossible to get out. A gas canister is able to incapacitate Chris before Max is abducted at gunpoint by an unseen man -- setting up the Season 3 finale stakes. The last episode will be all about rescuing Max (as Chris's problem is much easier to solve and putting Thomas behind bars.

It's a solid ending, because Owain Yeoman does his best to seem as smarmy and evil as possible in an almost "blink and you'll miss it" guest appearance. The former star of CBS' undervalued procedural The Mentalist can certainly play a bad guy; he's done it before. And Thomas is a classic bad guy archetype: the rich, powerful businessman who needs to be taken down. Putting Max in peril provides automatic tension as well as a personal stake for several other characters. But most importantly, this sequence of events injects a jolt of energy back into CSI: Vegas Season 3. The robot storyline has been relatively slow-moving since its introduction; fans needed something that would get them scared or excited, and those final moments accomplish both at the same time.

If CSI: Vegas has had a weakness over its three-season run, it's that the long-term storylines it incorporates haven't been as successful as its standalone cases of the week. The first season was more tightly plotted, but also an anomaly because it felt more like a limited series. Once the show continued into Seasons 2 and 3, the idea of having an ongoing mystery each season was admirable but proved to be hard to pull off. With "Heavy Metal," the show has the opposite problem. It sets up what should be a reasonably satisfying conclusion to the Truman Thomas story. What doesn't work as well is the case that comes before it.

CSI: Vegas Devotes a Whole Episode to Penny Gill

Season 3, Episode 9 Focuses on Penny's Development

CSI: Vegas Season 3, Episode 9, "Heavy Metal" follows the unintentional pattern of the last few outings: it feels more focused on coming up with a quirky or strange murder idea than developing the underlying story. This episode is stronger than its predecessors because the idea of killing a man with an electromagnet is genuinely interesting, but audiences are still likely to guess the killer before the show reveals it, given that there are only three significant guest characters introduced and one is never a suspect. With its angle about an old rock band, the story is a bit reminiscent of Midsomer Murders Series 10, Episode 4, "The Axeman Cometh," except that part comes in too late to dig into the history of the band and CSI has a much lower body count.

The biggest issue is that the episode is driven by Penny Gill. It's not just giving Penny a chance to be fleshed out further; everything orbits around her. The main plot is about her leading her first homicide case. The subplot is about a sudden tension that's developed between Penny and Chris, which is connected to Penny's engagement to Jack. None of this is compelling enough, and that's even more glaring since viewers know this is the second-to-last episode of the entire show. Penny is fine as a supporting character -- the dropped arc about her being mentored by Marg Helgenberger's fan-favorite Catherine Willows had potential -- but she's not interesting enough to be the lead, despite actor Sarah Gilman giving a ton of effort. It doesn't help that the two people most supporting Penny in the hour are Chris and Beau Finado; all three of those characters fit into the same general "quirky CSI" mold, so there's no contrast.

Penny Gill: Maybe your next partner will enjoy your sense of humor.

The subplots don't get off the ground either. Penny and Jack's relationship has never held the audience's attention, for all of the reasons that Chris articulates to Penny. Audiences haven't seen enough of Penny and Jack together to care that they're dating, let alone engaged, and the pairing doesn't have any impact on the overall show (unlike the romantic tension between Josh and Allie, which would significantly affect the whole Las Vegas Crime Lab, as Allie makes reference to when she tells Max that she and Josh "have eyes on us"). Chris and Penny's feud is only noteworthy for how it gets Allie to question her leadership abilities -- and Max to reinforce them. Otherwise, nothing is gained here, which is in sharp contrast to how CSI: Vegas has often truly pushed its characters in new directions.

Is CSI: Vegas on Track for a Proper Series Finale?

Penultimate Episode Suggests the Show's Return to Basics

Maxine Roby: Change is hard, not bad.

Despite the standalone plot not having enough dramatic momentum, CSI: Vegas Season 3, Episode 9 does suggest that the show can have the strong series finale it deserves. The closing minutes -- and a few brief scenes scattered throughout -- go back to the series' biggest strength, which is its characters and the well-established dynamics between them. The lack of complexity in Penny's story highlights how underdeveloped she is in contrast to the interactions between Max and Josh Folsom, whose mentorly relationship has been steadily grown and changed since the first season. In "Heavy Metal," Folsom wants to help Max as much as he can, and is visibly discomfited when she pushes him back. Matt Lauria doesn't get a ton of screen time but he says a lot with his reactions, but the fact that Max wants Folsom to be the one in the Crime Lab having her back is very telling, too.

Based on that setup, audiences can presume that Folsom will lead the charge to recover Max, which also sets up a wonderfully full-circle moment for his individual character arc. In the CSI: Vegas Season 2 finale "Dying Words," he was a homicide suspect; now in the Season 3 finale, he's hopefully not only going to be a hero again -- but be saving one of the people who means the most to him. If he can save Max, that might be the last piece Folsom needs to complete his redemption story. The moment between Max and Allie is important, too, because all of Allie's Season 3 arc has been about her becoming day shift supervisor and not feeling comfortable in that role. With Max missing, she has rank; does the season (and the series) end with her running the entire Crime Lab and finaly seeing what she can do? The pieces are in place for a few characters to take major steps forward at the end.

"Heavy Metal" will not have a ton of rewatch value, and CSI: Vegas would have benefited from spending more time on the Truman Thomas story or even more time with Thomas himself, to make the audience that much more excited about his fate. But it does indicate that the show knows what characters and relationships are its strongest, and where it needs to go to deliver a conclusion that works for those characters and the viewers watching at home. Whether or not it effectively ties off enough to make for a complete series finale is up in the air, yet if it sticks on this path, fans should feel like Max, Josh, Allie and everyone else have stopped in a good place.

The CSI: Vegas series finale airs May 19 at 10:00 p.m. on CBS.