Skins packed all its drama last week into the final nine minutes – Freddie confronting Effy's therapist, Dr John Foster, and being brutally murdered by him with a baseball bat. The signs prior to that moment that such a violent act would occur were scant; a brief flash of malevolent eyes from Foster earlier in the episode, the unsettling nature of his therapy sessions with Effy.

Then bang. Freddie was dead. And this week, for the finale, it was as if the event had never happened for 80% of the episode. The rest of the gang wondered where Freddie was but his sister had found a note that he had gone away for a bit and, while she encouraged Cook to search for him, by the second half of the story, everyone was collected in Freddie's shed having a party in his absence.

Effy was still at the mental hospital at the start of the episode, unaware of what Foster had done. He told her he was leaving his job and did. She didn't question that and returned to be with the rest of the characters, suddenly calmer and more together than during the whole of last week's episode. It seemed as though once her mental issues had served their purpose, they dissipated again.

No one was really that perturbed by Freddie's absence, it was simply used as a way to bring the rest of the Skins ensemble together. They gathered to celebrate his birthday without him and the loose ends were tied up clumsily. This Skins finale felt like the writers had simply run out of steam.

Surprise! Pandora was actually super-smart, took exams in secret and is headed to Harvard. Wham! Thomas was expelled but his skill at running gets him the chance of Harvard scholarship too. Boom! The police raid Naomi's house but Cook manages to evade them again because they don't post anyone at the back door.

While glimmers of genuine emotion remained – Naomi's speech to win Emily back was touching as she admitted her sarcastic front was only ever a shield to protect her from the intensity of her feelings – but the finale followed on from the rickety plotting of the previous two weeks.

The Skins writers used the Spooks technique of unexpectedly bumping off a major character but they shied away from dealing with the consequences. This series finale was choppy and uneventful until a sudden rush of activity at the end. The boozing, the drugs, the sex and the crying we've come to expect were all there for the majority of the episode but they all added up to very little.

It was in the final moments of the episode when Cook, spotting John Foster outside Freddie's house, trails him to the clinic and breaks in, that the one truly intense moment of action happened. Finding Freddie's bloodied clothes, Cook was confronted by Foster who was once again wielding his baseball bat. He demanded that Cook kneel for him to swing the bat but unsurprisingly Cook didn't do it.

With the final words of the series ("I'm Cook"), he threw himself at Foster and the screen went blank before the credits rolled. It was Skins taking the Sopranos approach to endings. Just as it's possible to wonder what happened to Tony Soprano, we'll be left wondering whether Cook survived his tussle with Foster.

This generation of Skins was arguably populated with more interesting and well-rounded characters than the first. But here, the writers did their creations a disservice. Their actions were often confusing and the plots were frequently paper thin – Cook's escape from prison and Foster's murderous rage were just the most obvious examples.

Skins' third generation obviously has potential - that's the great thing about constantly refreshing the cast - but the writers should rein in there taste for surreal montages set to Eighties tunes and sudden surprises that don't fit with the character: Effy, cool as ice for four series, breaking down for two episodes. Pandora ditzy for two series, super-scholar for one episode.

Skins doesn't need to be reality but we've got to at least feel it's plausible...