Der frühere Navy SEAL Thomas Magnum lebt in einem Gästehaus auf Robin’s Nest, dem luxuriösen Anwesen, für das er als Sicherheitsberater tätig ist und von wo aus er seinen Hauptjob als Privatdetektiv ausführt. ‚Majordomo‘ des Anwesens ist die frühere MI:6-Agentin Juliet Higgins, die ständig versucht Magnum im Zaum zu halten.

Magnums beste Freunde sind Theodore „TC“ Calvin, ein früherer Helikopterpilot der Marine, der nun Touristen Hawaii von oben zeigt, und Orville „Rick“ Wright, der als Betreiber des coolsten Nachtclubs von Oahu immer über die besten Kontakte verfügt. Auch wenn sich Magnum immer wieder in polizeiliche Ermittlungen einmischt, muss sich Detective Gordon Katsumoto eingestehen, dass er und der Ex-Marine sich in vielen Dingen ähnlicher sind, als er zunächst zugeben will.

Ein Thunfisch im Wert von 350.000 US-Dollar ist verschwunden, was seinem Besitzer, einem ums Überleben kämpfenden Fischer, schwer zu schaffen macht. Der Mann ist zudem ein früherer Kriegskamerad von Magnum und so begibt sich der Privatschnüffler natürlich auf die Suche nach dem 150 Kilo schweren Diebesgut.

Privatdetektiv-Kollege Luther Gilles bitte Magnum um Unterstützung bei einem besonders kniffligen Fall. Er soll die wahre Identität einer Frau klären, die im Koma liegt, deren Verlobter aber erfahren hat, dass ihr Gesicht einer größeren kosmetischen Operation unterzogen wurde.

Ein Kunstsammler heuert Magnum an, um sein Sicherheitssystem auf Herz und Nieren zu testen. Als der enge Freund von Higgins ermordet wird, wird ausgerechnet Thomas zum Hauptverdächtigen.

TC asks Magnum to take on a case to help acquit the father of one of his young football players, who is accused of murder.

An aging tycoon asks Magnum to find his lost love who he says just recently contacted him; the only problem is she died 30 years ago. Also, Rick and TC meet a fellow vet who is having a hard time adjusting to civilian life.

Magnum takes the case of a little girl’s missing cat and, in the process, stumbles upon another cat’s murdered owner who happens to be an FBI agent.

A man dying of lymphoma hires Magnum to find his estranged, bone-marrow-compatible brother who turns out to need Magnum’s help as well. Also, Magnum’s case brings back haunted memories for the guys of a past SEAL team mission that went sideways.

After a 16-year-old kidnap victim, Amanda, escapes her captors, her parents hire Magnum, who experienced similar trauma as a POW, to find who took her.

Magnum must help Rick’s crush, Toni, after her illegal poker game, organized to pay back a mob debt, is robbed by masked gunmen.

As Magnum helps a woman find her missing cousin, Sergei, a Russian fugitive, Higgins' and Kumu's lives are put in danger when they get too close to the case.

Magnum has an emotional connection to a case when he and every other private investigator and bounty hunter on Oahu are tasked to track down a man accused of murder.

Magnum and Higgins are shocked when one of her former MI6 teammates shows up with a fresh gunshot wound and news that "the Viper," the assassin who killed Higgins' true love, has surfaced on Oahu. Also, while Magnum's busy helping Higgins track down the Viper, he asks Rick to take over a case, a task that Rick relishes until it goes sideways.

A man hires Magnum to investigate his own murder before he is killed. Kumu reconnects with an old friend.

Magnum discovers that his ex, who landed him and his friends in a POW camp, is on the island and planing to steal a fortune in gold.

Magnum is hired by a woman to prove that her son didn't kill his girlfriend and has only 24 hours to do so before the accused accepts a plea deal. Also, Rick and TC try to recover stolen appliances that were donated to a wounded veteran.

After a man is murdered, Magnum poses as a doctor on the same dating app the victim was using in order to find the killer who may be praying on wealthy men.

When the Dobermans dig up what appears to be a human bone, Magnum and Higgins help Katsumoto investigate the murder of his former mentor.

When Magnum and Higgins get “yacht-jacked,” Higgins is shot and she and Magnum are stranded at sea, struggling to reach land before she bleeds out and the culprits return to finish them off.

Hannah, Magnum's ex and the fugitive responsible for him and his SEAL team brothers being POWs for years, shows up at his home with a gunshot wound, and wanting his help to find her missing CIA father whose life is in danger. Also, Magnum makes an earnest proposition to Higgins for her to become his private investigations partner.

While Magnum waits for Higgins to decide if she’ll officially become his partner, he takes the case of a missing wife who witnessed her boss’ murder during a bank robbery. Also, Rick makes a big decision about his career.

An incorrigible pickpocket, Jin, asks Magnum for help when a cell phone he recently lifted receives a very suspicious text message. Also, Magnum is frustrated when Higgins still won’t give him an answer to whether or not she will become his partner, and when Rick decides to make a bold career move, T.C. comes to the rescue.

Kumu and Higgins are in danger when Robin's Nest is under siege by mercenaries storming the estate in order to find out the true identity of the White Knight, Robin's muse and literary hero. Also, Rick and T.C. helps one of Rick's employees when his car is stolen, and Higgins finally gives Magnum an answer about if she'll become his partner.

When Katsumoto suspects that one of his fellow cops is dirty and has stolen evidence, he begrudgingly asks Magnum and Higgins for help. Also, Rick and TC help Los Angeles Rams defensive tackle Aaron Donald when his tablet, that contains the Rams’ playbook is stolen.

On Halloween, Magnum and Jin search for a skip-tracer at a Halloween bash, just as Katsumoto tracks an escaped killer who is headed to that same party. Also, Higgins and Rick must spend the night at an allegedly haunted house in order to debunk the notion, and TC and Kumu protect a sacred Hawaiian burial ground.

Magnum must help his defense attorney girlfriend, Abby Miller, when she realizes that the client she successfully defended in a murder trial is actually guilty. Also, TC confronts Kamekona about stealing his helicopter business.

While Magnum helps out his friend Russell Harlan and temporarily works as the head of a hotel’s security, he investigates the death of a guest who was thrown from her room’s balcony while working on a secret investigation of her own. Also, Icepick is released from jail and is trying to keep a secret from Rick.

Magnum and Higgins' new partnership is tested when they disagree about being hired by a woman who wants them to recover her $3 million in stolen drug money in order to save her husband's life.

A guilt-ridden Magnum follows the clues his private investigator friend, Harry Brown, left behind when he was shot while working a case Thomas passed onto him. Also, TC helps Kumu lead a protest against construction on a Hawaiian sacred site.

Magnum, flooded with memories of his tour in Afghanistan, helps his fallen friend’s brother search for a now-grown Afghan boy who may have been a victim of trafficking.

Magnum is called up from the reserves for a top secret mission, but his friends are stunned when they learn that the mission is a lie and Magnum has been set up.

When Junior is kidnapped as leverage to retrieve the stolen list of undercover CIA agents, and most of Five-0 is rounded up by the CIA to prevent them from interfering, Tani and Quinn ask Magnum and Higgins for their help.

The crossover starts on Hawaii Five-0 S10E12 Ihea ‘oe i ka wa a ka ua e loku ana? (Where were you when the rain was pouring?) (I).

Magnum and TC go undercover as efficiency experts when a corporate manager is murdered and everyone in the office is a suspect. Also, Rick is curious why Higgins faked an injury to prevent her from investigating the case with Thomas

When Jin learns that an innocent woman is the target of a deadly hit, he asks Magnum and Higgins to help save her.

Magnum and Higgins must find Kumu when she's kidnapped by an injured man accused of killing his wife.

While Magnum and Higgins are undercover as a couple on a romantic bus tour working a case, they must switch gears when one of the love birds on the trip is murdered and evidence is quickly deteriorating in the Hawaiian heat.

Magnum and Higgins take the case of recovering the stolen urn of a woman's deceased husband, but they soon find that others believe the urn is worth killing for. Also, Rick and TC confront a man who's been impersonating football legend Andre Reed.

As their wedding day approaches, Magnum and Higgins help a modern-day Robin Hood who, thinking she was helping a school obtain needed supplies, unknowingly stole illicit drugs. Also, Rick helps a retired soldier with the difficult task of re-entering the work force as a civilian.

Magnum and Higgins are each hired by a different spouse who are in the middle of a contentious divorce to dig up dirt on the other, and Thomas and Higgins soon find themselves competing over resources. Also, Rick and TC look into the death of an unidentified man and must share the news with his estranged daughter.

Magnum and Higgins help Rick when his father figure, Icepick , just out of prison and battling terminal cancer, gets double crossed on one last score. Also, Magnum makes one last bold move to help Higgins stay in the country.