Tonight's season finale opens with several Mal Noche men getting gunned down at one of their homes. The killer isn't shown, but the gun he uses is an automatic weapon.
We cut to Horatio, Delko, and Frank examining the scene. None of the dead Mal Noche members are the one they're looking for, Antonio Riaz, the man who put out the hit on Marisol. Officer Jessop comes by and asks Frank who they're looking for, and he's briefed. He then tells Frank that he'll go and look around. As he searches the gas grill unit, he opens the cabinet door below, setting off a grenade by accident. It sends Officer Jessop flying into the air, killing him.
After the credits roll, we join Alexx taking a look at Officer Jessop's body. She pulls a grenade pin out of Jessop's back. Attached is a piece of string, making it obvious that this was a booby trap. Elsewhere at the scene, Calleigh and Wolfe talk about Jessop. Jessop started patrol just as Wolfe was leaving it. Calleigh examines one of the gun shells left behind by the killer. The bullets are Russian, likely fired by an AK.
At the crime lab, we see a number of federal agents getting off of the elevator. They make their way through the lab and talk to some of the lab techs and then end up in Maxine Valera's office and ask her to come with them for questioning. She would like to grab a few files, but one of the agents doesn't want her to touch anything. As they walk down the hallway, people look on, thinking she did something illegal. Dan Cooper comes out and tells Natalia that Maxine Valera must have been the mole, but she doesn't buy it.
Elsewhere in the lab, Delko briefs Horatio on Jessop's body. The explosives used was TNT, which makes sense, as it was a grenade which killed him. Delko has also tried to reconstruct the bomb, and he's concluded that when Jessop pulled open the cabinet door, he set off the grenade because there was a piece of fishing line connecting the door and the grenade pin. Delko then does a search to see if this matches any other bombings in the past. He's fortunate to come up with a result, a Mala Noche gang member, Carlos Santigo. He used a similar bomb on December 19th, 2005 in Tampa. He was deported, but it seems he may be back.
As Ryan Wolfe enters the an evidence collection room, he finds to people looking through evidence, and he's not sure who they are. A woman steps forward and identifies herself as Special Agent Heather Landrey. Ryan Wolfe isn't too thrilled about the feds being around the lab right now, so he explains how he's got evidence to process in regards to Officer Jessop's murder. In response, she tells him that she'll have to escort him with the evidence to make sure no one tampers with it. The other agent in the room comes across an envelope of evidence and hands it to Special Agent Heather Landrey. Wolfe's not pleased about them taking important evidence like that out of the box it was originally in. Special Agent Heather Landrey tells Wolfe that they received a tip from someone that someone had tampered with the evidence.
In a separate room at the lab, Maxine Valera is questioned by one of the feds, Special Agent Perry, I believe. It's revealed that she didn't follow protocol. She didn't count the money in the evidence envelope. After hearing from Wolfe that the feds have moved in on the lab, Horatio stops by and talks to one of the agents. Horatio doesn't want them there and frankly tells him that he wants them out. We learn that the tipster has informed the feds that $12,000 is missing from the evidence envelope. Delko enters the scene and tells Horatio that airport security has nabbed Carlos Santigo.
In the interrogation room that Valera was being questioned in, Horatio and Delko question Carlos Santigo. He was arrested at the airport because he had TNT residue on his left hand. Santigo tells them that he doesn't know anything about any bombs, but quickly changes his story when he learns that an officer was killed by a bomb. He admits that Riaz told him to do one final job, rig the gas grill with a bomb. He assures them that he didn't know a police officer was the target. They then ask him about where Riaz, but Santigo doesn't know where he's at, because the exchange of money was done via a wire transfer. Delko quickly gets out of his chair and moves the table a bit, scaring Santigo. Delko wants to know where Riaz is right now. Riaz is believed to be the one who called for the hit on Delko's sister, Marisol.
In the lab, Calleigh is bagging up some evidence to move to another part of the lab. She's being shadowed by Special Agent Heather Landrey, who steps out of the room to use the restroom. Calleigh walks over and talks to Horatio. She tells him that the weapon used to kill the Mala Noche was Russian, which the Mala Noche don't use. This means an outsider is responsible for this. Monica West enters the scene and asks Horatio about why he's asking for Memmo Fierro to be transferred. He tells her that he'd like to speak to Memmo about Marisol's death. She warns him about making the situation any worse than it already is. Calleigh has made her way back to the lab and is then joined by Peter Elliott. He's a little surprised by all of the feds in the building. She tells them about the $12,000 that is reportedly missing. Calleigh is then asked to come in for questioning.
Across town, Horatio joins Memmo Fierro. He wants information on Antonio Riaz's location, but Memmo wants protection in return. Memmo tells Horatio that he knows a man who may know where Riaz is, Rafik Omad. They did some business together, and Rafik Omad has a warehouse on Dodge Island.
The Miami Dade PD enter Rafik Omad's warehouse to search for any weapons. Rafik tells them that he ships decorative vases. One of the officers enters from another portion of the warehouse with a large automatic weapon, likely the same one used to kill the Mala Noche gang members.
Back in the interrogation room, Calleigh is being questioned by one of the agents. He doesn't go for the normal questions, he brings up personal matters, such as Calleigh's boyfriend's suicide and her father's drinking problems. Calleigh's less than thrilled with the line of questioning, so she tries to get him to change the subject. It works and they talk about normal procedures for evidence collection of money. She tells him that she photographed the money, counted it twice, and write down each serial number. She hands him her notes from the scene, which includes all serial numbers and photographs of the money.
After the interview, Calleigh and Maxine Valera talk in the hallway about being questioned. Calleigh's surprised by how much information the agents have on them. Valera's concerned about being accused of taking the money, since she didn't follow procedure, neglecting to count the money and write down the serial numbers. Aaron Peters is then shown being escorted to the interrogation room, so the feds are still are still looking for the guilty party.
Back to the interrogation room, we see Aaron Peters being questioned. He tells the fed that he followed all procedures. The agent then brings up the fact that Aaron didn't follow up on a report from a while back. He was concerned about Delko being in the crime lab when they were investigating a case involving Marisol. Aaron was concerned that Delko may have tampered with something. He tells the agent that the situation worked itself out. The agent asks Aaron if there were anyone in the lab that he would think would do something illegal like stealing the $12,000.
We immediately cut to Ryan Wolfe being questioned. It seems like Aaron pointed the finger at Wolfe. Wolfe was the last one to leave initials on the envelope of evidence, so it looks like he was the last to handle it. The agent questioning him then brings up the idea that Wolfe has an eye problem. Wolfe knows that he only told one or two people about this as a test to find the mole, and it seems he/she told the feds.
After the interview, Wolfe confronts Dan Cooper in the hallway. He pushes him up against the wall and accuses him of being the mole. Dan tells him that he had a few drinks with some feds a little while ago and he may have said something may have slipped out. Calleigh runs in and tells Wolfe to let him go. By now, a small group of people have formed to watch the confrontation.
Down at the PD, Rafik Omad is questioned by Horatio and Delko. He tells them that Riaz was paid to do something for him and he never delivered on it, keeping the money. Rafik went to the Mala Noche house to look for him and he shot the other Mala Noche members when they wouldn't tell him. The transaction took place in the financial district, which has cameras throughout.
In the lab, Natalia is rushing through and runs into Delko, causing them both to drop the things they have in their hands. While they pick things up, they talk about the feds questioning people. Natalia tells him that she's not been questioned and that she won't be. Delko then pieces things together and realizes she is the mole. He can't believe that during the entire time she's been there, she's been reporting on the lab.
In the interrogation room, Delko is being questioned by one of the feds, Agent Cole. He tells Agent Cole that he counted and printed all of the money, as accordance to protocol. Agent Cole then brings up all of the problems Delko has had recently, especially with his sister. $12,000 is very tempting, afterall. Delko tells the agent that the information that they got on him is because their mole, Natalia was sleeping with him. He then leaves the room, despite Agent Cole's objection.
Elsewhere in the lab, Horatio checks in with Dan Cooper, who has been examining the camera footage from the financial district. He was able to find Antonio Riaz in the footage, but he's also with a girl during some of it. Horatio asks Dan to leave and brings in Delko. He's shocked to find that the girl with Riaz is actually Marisol. Neither of them can make any sense of it, so Delko leaves to get Marisol's personal things.
We cut to Horatio and Delko in the lab. They're looking through Marisol's day planner. They use the date from the camera footage and compare it to the day planner, and the planner says "meet Diego for lunch." Horatio asks Delko to run a search on Antonio Diaz and see if Diego is an alias. Delko quickly does a search on his computer and he verifies that it's an alias. They then grab Diego's phone number from the day planner. Horatio knows that they can trace the phone number via GPS.
Horatio calls Antonio Riaz on the phone and there's a helicopter in the air. The people in the helicopter is tracking Diaz's location while he and Horatio talk. Diaz clears a few things up for all of us. He wasn't dating Marisol. Instead, he was selling Marisol drugs. Horatio tells him that he'll catch him, but Diaz tells him the only thing he'll see if a "fireball over Miami." The transmission ends before they can get a lock on Diaz's location.
In the lab, Horatio and Delko examine shrink wrap from Sharif Omad's warehouse. It appears that it belongs to a weapons case, specifically one used to house a shoulder-fired surface-to-air missile.
We quickly cut to helicopters in the vicinity of the Miami airport. Antonio Diaz has a plane in his sights just as Delko and Horatio arrive. Realizing that if Diaz fired his missile, hundreds of people will die, so Horatio shoots him in the leg. Horatio and Delko walk up to him and Horatio takes too shots at him, which scares him a little. Diaz promises Horatio that if he doesn't die, he will continue to kill people Horatio loves. Delko kicks him in the face instead of shooting him. The police finally arrive to arrest Diaz.
At the lab, Wolfe is accused of taking the money from the envelope, so he asks to see the evidence against him. He points something out to Special Agent Heather Landrey. There is a second piece of tape over his. Also, there's corn starch powder on the tape. The lab here doesn't use those kinds of gloves because it can contaminate the evidence. They're after the wrong lab!
Natalia catches up with Calleigh in the hallway. She wants to explain herself, so Calleigh stops walking and allows her to speak. We learn that Natalia only leaked positive news about the lab, nothing negative. Calleigh then receives a call from Wolfe, who thinks he knows who took the money. Calleigh tells him she thinks she knows who called it in. She then leaves Natalia.
Calleigh catches up with Peter Elliott in the lab. She accuses him of taking the money from the envelope. He wore powdered gloves and returned the evidence envelope $12,000 lighter. He checked out the evidence just recently, so he's the most likely suspect. She asks him why he cane back this morning and pretended to process the evidence. He tells her to put something back. He pulls out a bundle of bills. Calleigh just can't believe this. He won't admit to taking it, however.
Outside, Peter Elliott talks to his fiance, Monica West. He knows that she took the money. He tells her that she shouldn't have used all of the personal information he told her to start an investigation into the lab like that. She then admits to taking the money to turn the heat up on the lab. Calleigh then enters the scene. She convinced Peter to being a recording device during this discussion, so they have her admission to the theft on tape. Monica isn't exactly happy about this, especially from her fiance, for pete's sake. Two police officers enter and arrest Monica and take her away.
In the morgue, Wolfe is looking over the body of Officer Jessop. Wolfe places Jessop's badge on his chest and slides him back into the morgue's refrigerator.
In the cemetery, Horatio is visiting Marisol's grave. He's interrupted by Agent Park. He tells Horatio some very bad news. Riaz has given them some important information about a terror cell and instead of trying him here, they're deporting him. Delko then finds out about Riaz's deportation. They then decide it's time to go after him, even if they have to go all the way to Brazil to get him.