It's the stuff that would get Sherlock Holmes' adrenaline going.

But Benedict Cumberbatch was visibly "shaken" as he called police after realizing that he was the target of a female stalker.

"The 39-year-old actor is said to have alerted Met officers after a woman repeatedly turned up at the house he shares with his wife and baby in north London," said Daily Mail.

"He became concerned after the stalker left mysterious red ribbons at his home - on one occasion fastened to a window and, on a separate visit, tied to his car."

According to London's Mirror, the female stalker was issued a police information notice or PIN which prohibits her from contacting or getting near Benedict Cumberbatch.

"The star has also stepped up security at the London theatre where he is currently performing amid fears the woman may instead visit him there," it said.

While Benedict Cumberbatch has become used to his newfound fame following the success of "Star Trek" and "Sherlock," the female stalker has "crossed a line."

"Benedict is used to people mobbing him wherever he goes and he's a good sport about it," the source told Mirror. "But this individual has taken things to the next level and there was no option but to pursue official action."

The source continued, "Turning up at professional events is one thing, but arriving uninvited at the family home is quite another. It might be that she thinks it's ­harmless, but it does feel a bit sinister. Leaving red ribbons is obviously a bit of a game, but it does feel quite dark."

The UK's Metro magazine claimed that the red ribbons left behind by Benedict Cumberbatch's female stalker hold deeper significance because they refer to a case handled by the fictional Sherlock Holmes.

"In the 1887 book A Study In Scarlet, Dr John Watson uses a red ribbon to tie his case files together," it said. "Cumberbatch's co-star Martin Freeman has received death threats since appearing in Sherlock."