Shanghai, 1934. In an insect world parallel to that of humans, veteran Inspector Sun, a lone spider, leads his last mission against his archenemy the Red Locust, before embarking on a well-deserved retirement. His vacation aboard a Pan Am clipper between Shanghai and San Francisco comes to an abrupt end when millionaire Dr. Spindlethorp is found murdered. What begins as a routine case for Sun will ultimately decide the fate of humanity.
This movie contains examples of:
- An Arm and a Leg: Red Locust's trademark is biting off one of the legs of his adversaries, with Sun himself being a notable example. That Dr. Spindlethorp's corpse also has a missing leg is what clues Sun in to Red Locust's involvement.
- Big Bad: The Red Locust, the bug world's public enemy No. 1 and Sun's Arch-Enemy.
- Black Widow: Discussed and subverted. Arabella Killtop is a literal black widow, and is the main suspect when Spindlethorp is found murdered. However, it turns out she's not the murderer and wants to find the real culprit, and it's even pointed out that black widows don't always kill their mates.
- Broken Pedestal: Part of the reason Mr. Scarab backstabs Sun is due to having lost respect for him, as he once considered him a good detective but now views him as a bumbling fool.
- Clear Their Name: Sun has to do this for Arabella, who's the primary suspect in Spindlethorp's murder.
- Clueless Detective: Inspector Sun, as noted by others, isn't competent so much as lucky. He screws up, misses details, and unwittingly gets others hurt, but ends up on top anyways.
- Death Flight: Mr. Scarab attempts to throw Janey off the seaplane, but she's saved by Sun. He later threatens Janey and Arabella in the same manner upon revealing his true colors.
- Death in the Clouds: Dr. Spindlethorp is murdered during a flight to San Francisco, with the mystery centering around who was the culprit.
- Exit, Pursued by a Bear: Both Vatchu and Red end up getting devoured by a fish after plunging into the sea.
- False Friend: Mr. Scarab is a long-time friend of Sun, inviting him onto the seaplane when he misses his prior flight and supporting his investigation on Spindlethorp's murder. He later reveals he was just using Sun in the hopes he'd lead him to Spindlethorp's fortune.
- Family Extermination: Red's swarm destroyed Janey's entire family in his last rampage, hence why she attaches herself to Sun, as she has no one else left.
- Foreshadowing: When the assassin bug is first revealed to the passengers, he attempts to attack Lady Vatchu. He's later revealed to have been hired to protect Arabella from "a monster", foreshadowing that the monster in question is Vatchu.
- Friendly Neighborhood Spider: They're the primary law enforcement of the bug world.
- Hive Queen: Lady Vatchu was created to serve as this for the Red Locust's new swarm. Upon consuming the formula to transform her into a queen, she's able to turn other bugs into hybrid bugs and command them.
- Hybridization Plot: The Red Locust is revealed to have had Dr. Spindlethorp create a hybrid bug queen that can transform other bugs into his hybrid swarm and Take Over the World.
- Hypercompetent Sidekick: Janey actually turns out to be this upon becoming Sun's unwanted sidekick. She picks up clues that Sun doesn't notice and is the one who ends up piecing together most of the conspiracy near the end. The Red Locust even mocks him by pointing out that his supposed "apprentice" was the one who figured everything out instead of him.
- I Work Alone: Sun repeatedly rejects Janey's offer to become his sidekick on the grounds that he "hunts alone".Sun: I'm a huntsman spider, and huntsmen hunt alone.
- Light Feminine and Dark Feminine: Janey is a sweet and bubbly Genki Girl (light) in contrast to the cold, aloof and sultry Arabella (dark).
- The Lost Lenore: Sun's wife was killed in a burglary gone wrong, with Sun having not been there due to being too busy trying to catch the Red Locust. Her death only spurred his efforts to detain his Arch-Enemy.
- Love Redeems: Dr. Spindlethorp was working for Red Locust and helping to create his new, more powerful swarm, but upon meeting and falling in love with Arabella, he abandons Red's plan and attempts to destroy his work.
- Plot-Triggering Death: Dr. Spindlethorp's murder is what sets off the primary investigation that ends up uncovering the larger conspiracy.
- Rude Hero, Nice Sidekick: Sun is arrogant and standoffish, in comparison to his self-proclaimed sidekick Janey, who's a bubbly Genki Girl who only wants to help him.
- Sole Survivor: Janey is the only survivor of her family after the Swarm's last rampage resulted in their deaths.
- The Swarm: The Red Locust's gang was called this, but their numbers were reduced due to Sun's efforts. Red's plan in the movie is to rebuild his swarm, only more powerful than before.
- Unwanted Assistance: Janey insists on becoming Sun's partner and helping with his investigation, despite his insistence that he "hunts alone". However, she actually does turn out to be a huge help in solving the mystery.
- Villain Holds the Leash: The Red Locust uses Lady Vatchu, the hybrid bug queen created by Dr. Spindlethorp, to turn other bugs into his swarm and set them loose onto the world.
