What does that dramatic Line of Duty finale mean for the next series?

An investigation into that final corrupt officer

"Four dots, four caddies. Four involved in organised crime." That was the revelation from Steve in the closing moments of series five after he spotted Dot's morse code (yes, really) in the moments before he died. The corrupt detective was sending a message to AC-12 – and with one of the four caddies still at large, we can expect the gang to be on their tail in series six.

Mercurio has already spoken of his hopes for more series beyond the already commissioned sixth, which means it's unlikely this overarching mystery is on the brink of being solved. But thanks to the balaclava gang John Corbett infiltrated, we now know senior corrupt officers prefer to communicate via instant messenger. We don't know whether it was Gill or the final remaining caddy who was in touch with Lisa – but if it was our mysterious copper, we also know they have difficulty spelling "definitely"...

Whoever it is, we can expect AC-12 to be in hot pursuit when Line of Duty returns.

The return of Patricia Carmichael?

Anna Maxwell Martin may have made a surprise entrance in the latter stages of the series, but she was as strong an addition as Stephen Graham. Her character, DCS Patricia Carmichael, was deliciously horrid, gleefully lobbing accusations at Ted during his various interrogations. She's also been a major hit with fans...

As we ended the series, Carmichael was seriously stroppy at her failure to sink Ted. The ambitious DCS still hoped to pin responsibility for John's death on him, but DCC Wise shut her down pronto, making a dig at the actions of Carmichael's sergeant Tina Tranter: "You had a bent officer on your team. Glass houses..."

Carmichael has unfinished business – and we'd love to see her wield her powers of interrogation once again in series six.

Will the OCG track down Gill and Lisa?

Over the course of Line of Duty, we've been told repeatedly that no one escapes this particular organised crime gang. Tommy Hunter took witness protection and was gunned down in the opening episode of series two; Jimmy Lakewell opted for a prison term instead of assisting a police inquiry. "There are some people there’s no immunity from," he reminded Steve at the end of series four.

So, it was a little peculiar that – as series five drew to a close – we saw both Gill Biggeloe and Lisa McQueen leading new lives with new identities. Surely their escape won't be that easy?

Lisa herself once told John: "Tommy got immunity, witness protection – the works. We still got to him. That's what happens to a rat."

Could series six see her and Gill silenced for good?

Steve and Kate's personal problems

Much of series five dug into Ted Hastings' domestic issues. With his life savings gone for good and his wife seeing someone else, the AC-12 boss was living in a grotty hotel with little semblance of a personal life.

But throughout the series, we were also given glimpses into the home lives of Steve and Kate. The latter was seen as the picture of domestic bliss in episode one, reunited with her husband and – thanks to her promotion – home in time to kiss her kid goodnight. But it didn't last. AC-12 is no nine to five, and the closing moments of the finale saw Kate home too late to see her family, once again. We sense her domesticity will be short-lived...

Steve, meanwhile, has been particularly unhappy since a balaclava man threw him down a stairwell. He's out of his wheelchair in series five, but a brief reunion with ex-girlfriend Sam Railston saw him unable to, ahem, perform. He ended up locked in the bathroom, crying, and by the series finale he was pictured home alone, popping painkillers. Will his habit develop into a full-blown addiction next season? Will he be seen addressing his problem?

Line of Duty rarely offers more than brief snippets of officers' personal lives but we sense Kate and Steve are set to suffer more unhappiness at home next time around.

Will Ted continue to look suspicious?

Series five was rough on Ted Hastings. The once upstanding AC-12 boss has operated under a cloud of suspicion all series, only exonerated by Steve and Kate towards the end of the finale.

But there are still some black marks next to Ted's name. Are we to belief he had time to study the linguistic patterns of the corrupt officer communicating with Lisa and John, replicating them with his own spelling of "definately"? Can we ever be sure he didn't tip off Lee Banks? We've rounded up all the evidence still hanging over Ted – and we find it hard to believe his slate will be wiped clean come series six.

Ryan rising through the ranks

In the closing moments of series five, OCG member Ryan Pilkington was pictured in a police training academy, having been accepted into the force. The rot doesn't stop with the current cohort of bent coppers – there's a new generation rising through the ranks.

With their numbers depleted – Dot, Hilton and Gill have now all been unmasked – Ryan will no doubt play an important role in the future of the criminal group. Like Dot, he grew up within the OCG – we first came across him in series one as a youngster...

And he used his run-ins with the law in his police interview –

"The person that made me see there was another way to be a useful member of society was a police officer – PC Simon Bannerjee. He's the reason why I wanted to become a police officer, too. To help people."

But after his murder of John, we know Ryan's capable of being chillingly ruthless.

A new guest star

Five series in, Line of Duty has built up an impressive roster of guest stars – from Lennie James and Keeley Hawes to Thandie Newton and Stephen Graham. Anna Maxwell Martin's Patricia Carmichael lives on, but it seems likely Ted and the team will be joined by a new guest character next time around...

Who should it be?