Season 2, Episode 21:

Zero Day

"Can you hear me?"

— The Machine

After ten days of silence, the Machine gives Finch and Reese the number of Ernest Thornhill, a mysterious tech millionaire whose true identity is not what they expected. With fewer than 24 hours left until the virus infecting the Machine goes live, time is running out as old and new enemies appear, old secrets are revealed, and Reese and Finch find themselves forced to accept help from some unexpected allies as they race to stop the threat against Thornhill's life.

Tropes present in this episode:

Anachronism Stew: The most sophisticated computer on the planet resorts to manual data entry to protect the evolution of its AI.
Are We There Yet?: Finch compares Reese's frequent inquiries about whether the Machine has given them a new number to this.
Answer Cut: A Decima agent asks Greer where the payphone is. Cut to Root saying, "The New York Public Library."
Armor-Piercing Question: Nathan gives one to Finch:
Nathan: Do you even remember your real name, Harold?
Be Careful What You Wish For: Finch uses these exact words to Root.
Brain Uploading: Ernest Thornhill's data entry company is doing this for The Machine, so it can preserve non-relevant memories from its nightly reboot. Root, horrified, calls it an external hard drive made up of people and paper.
Call-Back: Several, but most notably:
- Nathan's comment to Finch in a flashback—"Nothing is ever simple with you, Harold."—echoes the conversation between Reese and Finch in the diner in "Judgment."
- A "Panther platform" sedan built by Ford Motor Company flips over on its roof in a crash, as occurred in "Pilot" and "Firewall."
- The episode ends with a shot of Reese answering a pay phone call from The Machine like he did in the season 1 finale, "Firewall." His posture and facial expression are identical.
- On showing Nathan's board in the Library the camera lingers on Anna Sanders, the woman we saw him following in "One Percent".
- Finch describing libraries being shut down as "The decline of Western civilisation" happened in the pilot.
Calling the Cops on the FBI: Finch sends Reese to investigate Thornhill's apartment and then calls the police on him so he won't interfere with him meeting Root.
Chronic Hero Syndrome: The Numbers have stopped coming, but Reese is listening to a police radio, hoping to avert at least some crimes.
*Click* Hello: This is becoming a bit of a Running Gag between Reese and Shaw.
Complexity Addiction (Or Manipulative Bastard): As lampshaded by Nathan and Finch himself.
Nathan: There's always two layers to what you do.
Crazy-Prepared: Reese reveals that he planted a tracking device on Finch's glasses at one point because he doesn't want to risk losing another person that he cares about.
Cut Phone Lines:
- Decima has every payphone in Midtown under surveillance, waiting to see if Finch turns up.
- The Machine tries to warn about the attempt on Carter, but Root prevents Finch from answering, and Reese has just been arrested.
Death from Above: A highly innovative version. An assassin uses an RC UAV packed with some explosives and flies it into the sedan the POI is being chauffeured around in.
Declaration of Protection: Reese promises Finch that he won't let Root get to him again. So of course Finch then sends Reese out to do some bogus recon work, calls the police on him and goes to meet Root anyway.
Dramatic Irony: Nathan demands to know what Finch would say to the next person on the Irrelevant list after Finch deletes it. Finch replies that he would tell that person he was sorry. Moments later he says to Nathan, "I'm sorry, but you can't save everyone" unaware that Nathan's name has just come up.
Enemy Mine: Finch ends up having to team up with Root to protect the Machine.
Facial Dialogue: Reese engages in some fantastic non-verbal communication when Shaw asks if he is able to track down Finch.
First-Name Basis:
- Root tells Finch to call her by her assumed name. After hearing this, Harold continues to address her as "Ms. Groves".
- Inverted with Greer using Reese's and Shaw's last names, to show he knows all about them.
Foreshadowing: Root expresses envy over how Reese has tracked Finch down again, saying "I wish I had a pet." Shaw takes on her Reese role in future seasons.
Frame-Up: Carter is framed for shooting an "un"armed man.
Freeze-Frame Bonus:
- At the very end of The Machine's reboot sequence, there's a block of binary code.◊ If you convert it to ASCII, it reads Quis custodiet ipsos custodes—Latin for "Who watches the watchers?"
- A newspaper clipping pinned to Anna Sanders photograph shows that Nathan saved her from a stalker who was planning an abduction.
Genius Bonus: Finch says the Machine deletes itself and "reinstantiates 1.618 seconds later" every midnight. 1.618 is the "golden ratio."
I Have Your Wife: Finch agrees to go with Root after she explicitly threatens Grace.
Indy Ploy: "This is the plan."
Interface Screw: The Machine suffers from this big time due to the virus.
I Resemble That Remark!: Carter says that Thornhill is either extremely paranoid or taking lessons from Finch, who deadpans, "I would never book a car service under my own name."
Just a Machine: Finch regarding his creation. It started to evolve, but as this isn't what was required, Finch had the Machine delete its memories along with the irrelevant list.
Like an Old Married Couple: Shaw and Reese bicker over who's driving the car while busting out of the police station.
Lampshade Hanging: Nathan hangs a lampshade on Finch's tendency to choose bird names for aliases.
Nathan: You don't think [Grace] will consent to be Mrs. Ostrich?
Make It Look Like an Accident/Frame-Up: Terney is about to shoot Carter In the Back during a police raid, when the suspect bursts out of the house and she shoots him in self-defense. Terney quickly adapts by removing the gun from the scene, and telling IAD that he never saw if the suspect had a gun.
Mook Chivalry: The big mook has a knife under John's throat and... instead of killing him, just waits until John kills him instead. Reminds of infamous Darth Maul vs. Obi Wan suicide-by-inaction scene.
Nerves of Steel:
- The Special Counsel keeps his cool when his secretary pulls a gun on him.
- When Shaw and Reese are killing off Greer's security detail, he's calmly finishing off some paperwork he's been examining, chats with the two badass assassins who have every reason to kill him and when reinforcements arrive, slips away.
Nice Job Breaking It, Hero:
- Finch shuts down Nathan's connection to the Irrelevant list, just as Nathan's name comes through.
- Finch arranges for Reese to be arrested, so when Root stops him from answering the phone, there's no-one the Machine can contact to save Carter. Fortunately she's quick on the trigger.
Noodle Incident: Nathan alludes to whatever events caused Finch to take on a new identity in the first place, implying that he would be charged with sedition and mayhem.
Not So Stoic: Greer is glad to note the reaction on Reese's face to the name Harold Finch, the mystery man he's been seeking.
Offscreen Moment of Awesome: Nathan Ingram, middle-aged engineer and businessman with no combat training, saving the lives of five people, with little more than a handgun and a sense of justice.
O.O.C. Is Serious Business: Finch is much more vague and reclusive in this episode than usual and is sort of played up to be a villain. It's because he knows exactly what happens to the Machine when the virus hits zero (he even is responsible for the virus's existence) and has to team up with Root, something Reese would never approve of, to protect the Machine from the consequences.
Perma-Stubble: Reese has been sporting this during the past few episodes.^note
Real Life Writes the Plot: Kevin Chapman landed roles in two feature films, and wasn't available when the last two episodes of Season 2 were being shot.
Shame If Something Happened: Root threatens to take Grace out for coffee if Finch doesn't cooperate.
Shout-Out: The bald-headed assassin to Hitman. Also Ernest Thornhill (see The Spook).
The Sociopath: Root denies being this. Why, it would be a lot easier to murder and manipulate people if she was!
Special Edition Title: The Machine is unable to show the intro due to the virus. It gives up after a few tries and skips to the Previously on….
The Spook: Ernest Thornhill, whose name is a Shout-Out to two other famous works involving an invented person, The Importance of Being Earnest and North By Northwest.
Stealth Hi/Bye: Reese isn't surprised when Shaw disappears during the police raid, though he is when she turns up pretending to be his lawyer instead of Finch.
Tearjerker: Everything about the flashbacks. Everything.
Tempting Fate: Harold says he would look the next victim shown by the Irrelevant List in the eye and tell them it was for the greater good. He's saying this while looking Nathan in the eye, as the Machine is about to reveal his number.
Title Drop: Harold gets awfully close to it in one of the flashbacks.
"...So technically it would still be day zero."
We Used to Be Friends: Finch contemptuously refers to Nathan 'drinking away' whatever software skills he had, and refers to the Machine as something he, not 'they', created.
Wham Episode
Wham Line:
- Finch: Ernest Thornhill...is the Machine!"
- The Machine: Can you hear me?
What the Hell, Hero?:
- Finch gets one from Root, of all people, after explaining what he did to limit the evolution of the Machine's AI^note. She shows far more emotion over this than she has over any of the five people she's known to have murdered.
- Finch is aghast at the security breach caused by Nathan establishing a backdoor into the Machine.
When the Clock Strikes Twelve: The virus is set to go live at midnight.
With This Ring: Finch proposing to Grace, with a ring inside the mock cover of a Jane Austen novel.
Written-In Absence: Fusco was absent from "Zero Day" and "God Mode", and Carter mentions early on that it's because he is working a case elsewhere.