In a mystery worthy of the master detective himself, the BBC is investigating the possibility that the final episode of its hit sleuth series Sherlock, starring Benedict Cumberbatch and Martin Freeman, was illegally leaked online by a state-sponsored Russian TV channel in advance of its domestic screening Sunday night.

The leaked episode included a continuity announcement identifying it as “a Channel One” broadcast—the channel that has the Russian rights to Sherlock—and BBC insiders have been quoted telling British media that there is a widespread assumption that the leak was malicious.

There is speculation that Moscow co-ordinated the leak in order to demonstrate its capability to retaliate after a recent decision to expand the BBC World Service’s Russian-language output.

The Kremlin has also previously threatened reprisals against Britain’s public-service broadcaster after a British bank attempted to close down bank accounts linked to Kremlin-sponsored broadcaster RT.

In October, a spokeswoman for Russia’s foreign ministry said of the abortive attempt to close RT’s accounts: “Our stance is straightforward: We will stick up for our own. They [Britain] will get as good as they give.”

A BBC insider told the Telegraph: “We have brought [security] up to beyond gold standard, which is why things like this are so surprising. This is more than an accident.”

The BBC has said it is conducting “a full investigation” into how the leak has occurred.

Channel One has denied any wrongdoing, claiming the program was stolen by someone outside the company.

“Initial investigations suggest our content system was compromised by an unauthorized external third party,” it said in a statement, “Channel One Russia has been cooperating with BBC Worldwide from the moment we were alerted to the appearance of the leaked episode and we are doing everything in our power to determine the source of the breach.”

Hacking the election’s one thing, but if the Russians start hacking our TV without even issuing spoiler alerts, this really will be a fresh chapter in the new Cold War.