Shetland could be about to lose a long-serving character as Eadie Tulloch's killer is seemingly revealed

Oh, Tosh.

BBC crime drama Shetland hasn't been kind to the detective, who was raped in season 3 and almost blown up in season 7, to name just a couple of extremely difficult moments in her life.

And season 10 has brought its own challenges too – namely, the discovery that Sgt Billy McCabe, who she has worked with for years and also considers a friend, is not the man she thought he was.

In tonight's episode (3rd December), Tosh went to meet him for a second time following an explosive confrontation that morning, in which she said she would go to Professional Standards with the information she had if he disobeyed her order not to come into work.

Billy's former sergeant was Robert Tulloch, who was also the husband of Eadie Tulloch, a former social worker who was found dead in her garden by her neighbour, Colin Waite, while he was checking in on her.

Billy and Robert — and their wives, who worked together — were also very close friends.

But as part of the investigation into Eadie's murder, Sandy uncovered some bank statements that pointed towards Robert being corrupt — there were several large cash deposits, and no income streams to account for those sums — and possibly Billy too, given that the statement he took from Sandy's desk also showed £10,000 paid into his account by Robert.

Billy initially told Tosh it was a loan to buy his house, but during their second conversation, the picture shifted again.

Eadie and Robert had two sons: Ed, who runs the pub and was estranged from his mum when she was killed, and Craig, who died at sea a number of years ago alongside the son of their neighbours Lana and Arthur Mair.

Their bodies were never recovered, but the boat they were on did wash up in a bay a few miles south — which Billy searched in the hope of "salvaging something personal" for Eadie and Robert.

But while he didn't find anything of that nature, he did uncover a sizeable shipment of heroin.

That information didn't make it into the police report, however, because Robert asked him to keep it to himself. And Billy, not wanting to cause him any more pain than was unavoidable, believing he was doing right by his friend, agreed.

"He was devastated. I wanted to help my friend," he explained. "There was nothing to be gained by making it public. Those boys were dead. What good would it have done to stain their memory?"

Two months later, Robert loaned Billy the money — which he did eventually pay back. But regardless of how Billy perceived his friend's actions at the time, it was a pay-off, plain and simple.

When a horrified Tosh then asked what had happened to the drugs, Billy said Robert had disposed of them. But he didn't know the specifics — and he didn't ask.

"Did Robert Tulloch sell them on?" she enquired. "Because that would explain where all his money came from."

But Billy, tears in his eyes, didn't have an answer for her, as he went on to admit that he did eventually start to become suspicious of Robert, beginning with the arrest of Ray Powell.

Ray was a local criminal who had admitted to a robbery at the docks a number of years ago — despite being innocent of that particular crime — after Robert threatened to have Ray and his wife Gina's son, also their neighbours, taken into care. And after a recent conversation with Gina, Billy was under no illusions that Robert was only guilty of "a few backhanders" here and there; his friend was a very unpleasant man.

"What are you going to do?" he asked Tosh after laying it all on the table , but in that moment, she didn't have an answer for him.

"I'm sorry, Tosh. I really am," he said, before he left, leaving the DI in floods of tears.

Regardless of Billy's supposedly genuine motivations at the time — or the fact it happened 20 years ago and he has seemingly played it straight ever since — his future on the force is now in serious doubt. Not to mention that corruption, tampering with evidence and perverting the course of justice could all surely be levelled against him, all of which carry jail terms.

There's also a question mark hanging over Billy's relationships with Tosh and Sandy in particular, which could well be tarnished beyond repair.

Read more:

• Shetland’s Ashley Jensen said her arrival as new DI could have “gone one way or another”
• Shetland’s Alison O’Donnell reveals why she cried after watching first episode following Douglas Henshall’s exit

And another relationship that looks set to be tarnished — before it's even really gotten going — is that of Calder and Ed, Eadie and Robert's son.

There was a hint of something to come between the pair when they first met — and the fact that Ed knew Cal, an old flame of Calder's who she reconnected with on returning to Shetland, also drew them closer together.

And at the end of tonight's episode, after enjoying an intimate drink together at Calder's house — Ed spoke about the death of his brother, while she confided in him about the attempted murder of recovering drug addict Will Louden, which she blames herself for, given she promised to overturn his shoplifting charge in exchange for evidence on drug dealing family the Callaghans — it looks like they ended up spending the night together.

But that appears to be a decision Calder will come to bitterly regret.

Shortly before they went upstairs, the stormy conditions outside were causing the DI's broken gate — which she'd long been meaning to fix — to bang, which was quite the mood killer. So Ed, ever the gentleman, raced outside (bad weather be damned), grabbed some thick rope from his car, and tied it shut — which, on the surface, sounds like a perfectly lovely thing to do, and totally innocuous to boot.

But of course, this is Shetland, which means everything means something. And in this case, the rope means absolutely everything, because the body of Ed's mother Eadie was found tied to her garden fence in much the same manner.

While it's already been acknowledged that more than one person in Shetland is handy with knots, there's no denying the spotlight is now firmly on Ed — especially given what was unfolding elsewhere on the isles at the same time.

Sandy and PC Alex Grant had gone to arrest Lewis Mitchell, the man from the fish and chip shop who's involved in drug dealing and had attempted to kill Louden.

After cuffing him, Sandy searched his bag and found drugs, a passport and, crucially, Louden's missing phone. Jackpot.

But just as they were about to take him to the station, Mitchell said he had a name for them.

"I've got information," he added. "About the Callaghans, who works for them."

Sandy then immediately called Calder — presumably to tell her Ed is now their prime suspect — but she was tied up herself, with the man of the hour, and likely would be for some time.

Then, just before the credits rolled, there it was again: Ed's elegant knotwork, as the storm raged on. But the real storm is undoubtedly yet to come.

Oh, Calder. You sure can pick 'em.

Shetland season 10 airs on Wednesdays on BBC One and BBC iPlayer. Seasons 1-9 are available to stream on iPlayer now. Ann Cleeves's Shetland novels are available to buy.

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