There were loose ends. We were promised they'd be tied up. There were mysteries. We were promised they'd be solved. There were interminable guesses as to what might happen and of course we knew that within the hour all the guessing would be over and we would know. So with breath so heavily bated we thought our lungs had set, 9pm rolled around and we were off...

As Sam's stand-in DCI, Frank Morgan had promised to "bring him home" as soon as they could. Sam had his number - Hyde 2612 - but had been warned off calling it. "You know the rules Sam: we call you."

But back in the future, Frank Morgan is really Sam's surgeon. And in an episode of Jim'll Fix It, moved especially to radio for the occasion, Jim is going to fix it for Frank to remove the tumour from Sam's head so that he can "go home." As far as Sam is concerned, the message is clear. Gene Hunt is the cancer that needs to be removed before Sam can get his life back. He's torn between wanting that, and wanting Annie, yet he can't pretend to her that he's going to stick around. He asks her to stay with him for just one night, but Annie is not a one-night kind of girl.

Sam's first chance to secure evidence that can convict Gene of professional misconduct comes after a miner is found dead and Gene "interviews" Donald Sykes (played by the first of tonight's Shameless refugees - Jack Deam). Under an interrogation that amounts to torture, the details of which are carefully recorded by Sam, Sykes reveals the murder was the result of an argument over a proposed heist involving miners' wages. The mastermind behind it is none other than notorious cop-killer Leslie Johns (our second Shameless escapee: Sean Gilder).

Gene plans to go undercover on the heist and catch Leslie Johns red-handed, but Sam can't believe he would put his team at such risk, and arranges to meet with Morgan to hand over his evidence. The meeting has more in store for Sam than he expected, and casts doubt on all his certainty about his "former life." Morgan tells him he was sent to A division undercover, working to clean out the corrupt department and then rebuild it as part of Morgan's special project: the Metropolitan Accountability & Reconciliation Strategy, or MARS. On his way from Hyde on the day of his transfer, Sam was involved in a car accident and is still suffering from amnesia as a result. As Morgan continues expressing his admiration for the way Sam discharged his responsibilities, Sam's world tilts on its axis. Morgan calls him Williams and shows him the graves of his parents, right next to those of Vic and Ruth Tyler whose names they used in concocting Sam's undercover identity. And the shocks don't end there. Right next to the graves of the people Sam thought were his parents is that of Sam Tyler himself, who died in 1881.

Rushing back to the station Sam searches frantically through his desk and finds his original transfer papers from Hyde - signed by Frank Morgan. As he stares at it in horror the strains of Atomic Rooster's "Decision/Indecision" swell into his consciousness and ours..."I'm going to find the way back home."

Stunned by these multiple revelations, Sam comes clean about his real reason for being in Manchester to Annie, Ray and Chris (much to their disgust) and tries to call off the undercover operation. But it's too late - Gene has already infiltrated Johns' gang - so the rest of A Division set off for the railway station, an uneasy truce established between them for the duration of the job, in the interests of getting Gene out alive.

With the train loaded up with wages, it's not long before Johns' gang bring it to a halt and demand the money be handed over. Before anyone can comply, a police radio falls out of Sam's pocket. The game is up and Johns and his gang open fire on our heroes. Gene dives for cover aboard the train in a hail of bullets. Sam can't raise Morgan on the radio and offers to run for back-up, promising not to abandon his team, but as he enters a tunnel a short way down the track, he finds Morgan there waiting for him, urging him to leave the rest of the team to be killed and seal Gene Hunt's fate. Sam can't believe Morgan would do that, and wrestles with his conscience, but Morgan doesn't give up trying to lead him into the light...of a hospital room, where Sam awakes from the operation to remove his tumour.  It's Room 2612 in Hyde Ward.

Back in the 21st century Sam visits his mother and relates his adventures. He records them on tape too, to be sent for psych analysis. They still seem very real to him. He tells his Mum how the barman, Nelson, explained to him how to tell if you were alive or not. If you feel it, you're alive. Back in the office, Sam is daydreaming. When his attention is called back to the meeting, a colleague points out that Sam has cut his finger. But he didn't feel it. Sam excuses himself and heads for the roof to clear his mind. If he can't feel the cut, is he really alive? With sudden determination, Sam runs for the edge and pitches himself off the roof of his office and...back into the tunnel, where Annie, Gene, Ray and Chris are all limping along the track trying to escape the gunmen. Sam takes aim and despatches Johns with two well-placed shots.

He came through for the team in the end, so all is very quickly forgiven and Sam tells Annie that this time, he's here to stay. When the radio tries to get his attention, Sam tunes to a different channel. He's made his choice.

The culmination of the nation's favourite adult science fiction drama of the last two years faced a hard task to meet the high expectations and for once, I have to say, a much-hyped programme did not disappoint. It excelled on all counts. The acting was first rate, especially from John Simm. The internal torture as he tried to come to terms with one revelation after another was clearly visible on his face throughout and quite remarkable. The plotting was deep and crisp and even, giving us plenty to get our teeth into and our minds around, leaving no visible holes and remaining consistently twistworthy for the whole hour. And the writing delivered right-on dialogue: funny, sharp, believable, and uncompromising.

Like all good science fiction, Life On Mars didn't *really* tie up all the loose ends. In the manner of 2001 A Space Odyssey, it left the ending sufficiently, one might almost say satisfyingly, ambiguous to allow for further debate among fans. Did Sam really just have an amnesiac episode in the tunnel during which he imagined he was back in the 21st century? Or was his life in the 70s really part of his coma, but in the end it was more real to him than reality, so he chose to return to it by jumping off a building and ending up either dead, or back in a coma? Was Morgan Sam's boss, or his doctor, or maybe even just his subconscious? (Edit: If you'd rather have answers than continuing debate, read Ian Wylie's excellent and exclusive interview with Life On Mars lead writer and co-creator Matthew Graham)

So, it's over. But again, like all programmes that we look back on with fondness and keen nostalgia, Life On Mars went out on an incredible high. We'll never be able to say "it was good once, but look what it's become." It WAS good. It was brilliant. Or even, in the words of my esteemed editor, it was brilliantly brilliant. And it will remain undimmed in our memory and on our DVD players for years to come. [John Beresford]