So, this is where we come to the end of the beginning, the first of a two-parter to end season 2 and change things for ever. The guest list runs on forever with names we know, the action is low-key but non-stop, the accent is on apprehension, the Machine is on the fritz, cracking in Finch’s opening monologue, breaking it down, breaking down. It’s Zero Day, the day Decima’s virus goes active at midnight and all the rules come up for re-writing.

There’s a nervy edge throughout as the Machine’s constant insertions flash, split into code, blur the sound, racket crazily about until you’re twitching just from watching it. Reese is twitching: there have been no Numbers for ten days (nor any Relevant ones either as ‘Miss May’ – our dear pal Root – deploys an unusual method of handing in her notice to Special Counsel). Reese is reduced to ‘ambulance chasing’, following the Police bands. He’s too late for this one, two Elias men, one innocent, but gets to speak to Carter, who’s determined to bring down HR, a decision that will have consequences for her.

But the game’s on, a Number forced out, Ernest Thornhill, millionaire owner of payphone companies, who seems to operate wholly on-line, whose company employs people to spend all day copying code out of one computer and typing it into another. Thornhill (are we remembering North by North-West yet?) even hires a car to drive nobody back from the airport, a car bombed by a drone, a drone set up by Decima Technologies.

The Machine, reeling it seems, goes into flashback mode. A whole Finch tells Nathan Ingram that he plans to ask Grace to marry him on her birthday. Nathan’s engaged in rebuilding the company after seven years non-profit work developing their ‘project’. Nathan’s also engaged in drinking a lot. It’s day 1 of a new life for Finch: no, the engineer in Finch corrects, Grace’s birthday is tomorrow. That makes today Day 0.

There’s a complication, brought up jocularly by Nathan, but there’s something else under his voice. Under what pseudonym will Harold marry? Will Grace become Mrs Ostrich? But Harold is intending to become his real self again, for the first time in a long time. That will cause certain legal problems. It appears Harold’s real self is still wanted for youthful transgressions: sedition, mayhem. Still, the company can afford good lawyers…

And Harold proposes to Grace, as far away from surveillance cameras as he can, and out of earshot, the whole bended knee. And she accepts.

Everything is turning, falling in upon itself. Root calls Finch on his mobile phone. Time is running out. Whatever’s going to happen will happen at midnight. Everyone except Harold seems to be in urgent mode. Only he knows better.  But despite John’s insistence on protecting him from the ingenious hacker, Harold goes to a meeting with Root without telling. He has to: it’s outside Grace’s home. Root has made friends with Grace.

So Harold Finch unwillingly starts working with Samantha ‘Root’ Groves. And, following the trail of Ernest Thornhill, a ‘ghost’, a non-existent person created as a front, John Reese starts working, a little less unwillingly, with Sameen Shaw, who’s still following Root’s trail.

Things start to converge. Finch spots Nathan Ingram acting suspiciously, follows him to his ‘lair’, a disused Library, discovers Nathan and his back door into the Machine, his non-Relevant numbers, his less than fifty percent success rate (hence the drinking). Finch is stern in his opposition to this use of the Machine, obdurate in the face of faces who will die without intervention, callous in his assessment of Nathan’s remaining skills, and permanently shutting down the access. Out he storms. The last Number the Machine issues before it shuts down is Nathan Ingram.

Root knows far more than she should about the Machine. Decima knows a hell of a lot of it too. At midnight, the Machine will shut down. It will undergo a hard reset and call a payphone. Whoever answers will be given total access and control over the Machine. Decima know this. Decima wants the Machine. They’re guarding all the payphones, they want ‘Thornhill’ dead because ‘he’ owns them. Reese and Shaw, tailing Finch and Root, meet Greer, a confident, dry, wholly composed Greer, who drops a bombshell: their virus was built from code in a briefcase, the briefcase, the Ordos briefcase Reese and Kara Stanton were supposed to retrieve/destroy. The creator of that code was a man called Harold Finch.

Meanwhile, Carter’s being taken out of the game by HR. Terney has a lead on Beecher’s shooter, but it’s a set-up, a raid in which he’s meant to kill her. But a shooter appears before them. Carter draws and kills him, a good shoot. But not when IAB arrive, and both the gun and Terney’s recollection of seeing it disappear like the morning mist…

And Root and Finch, ten minutes ahead. Finch is confident. Yes, the Machine will call a payphone at midnight. But only he knows which one. Except that Decima know it too. And there’s more. Root realises that the print-outs, the endless code recycling, ae the Machine’s memories. To limit the Machine, Finch programmed it to dump all its memories at midnight. Every day it is reborn. Root’s horror infects us. Every night, Finch kills the Machine. We anthropomorhise as much as she does, see the Machine as a person, not a thing.

It’s almost midnight. Appropriately, the payphone is in a Library. Everybody’s headed there. Root is determined to take the call, to enter God Mode, to free the Machine. Reese and Shaw are shooting Decima bad guys. Harold diverts the call to the payphone he and Root are at, by rewiring the junction box. At midnight the Machine shuts down. Two payphones ring. Root answers one, seems pleased with what she hears, drags Finch off saying that the fun starts now.

The other is answered by Reese. The voice of the Machine asks, “Can you hear me?”

On original broadcast, the audience had to wait seven days for the second part. Now, so do I.