No, The Watchful Eye is not based on a book. The Freeform series is an original story.

The book under a similar name, Under a Watchful Eye, was written by Adam Nevill.

However, the story of the series and the book are different. The Nevill novel is centered on Seb Logan. 

He had been watched by an unknown dark figure and became the victim of terrifying paranoia without acknowledging his bully. 

Another same-name book, 2005 The Watchful Eye by Wess Reed, also has a diverse story from the series.

Its focus is on an agency that tried to gather corruption information against the government. The Watchful Eye is the government computer program hacked by Adrian Jacobs.

The Wrap said the series has parts of the mysteries of The White Lotus and Mare of Easttown.

Nonetheless, the horror series focuses on the murder mystery in the hunted building, The Greybourne, where Elena got hired as a nanny.

However, she came with a different mission in the building with her lover. 

It shares the story of the suicide of Allie Wards and the new start of the Wards family's life after they hired a nanny whose emotional tale led her to the building in Manhattan.

She was searching for ruby in the building, so she maintained a good bonding with the neighbors and the families.

However, she heard a strange voice while she was on her mission. Previously, she heard it in the elevator while she went for an interview.

Even Allie's aunt Ivey found something fishy about Elena and asked her to put an eye on the Wards family. 

According to Collider, all the building's characters would be part of the coverup, sharing more tension and an exciting plot with mystery and secrets.

The first episode starts and ends with Allie Ward's mystery suicide.

The series begins with the suicide attempt of the girl who ends her life jumping from the floor after writing to her family.

The watchman spotted the girl's demise, and the story began six months later.

It starts with the new beginning of Elena Santos from Peninsula, who came to The Greybourne building to see the Wards for an interview.

Jasper's father, Matthew Ward, interviewed Elena. Next, Ward introduced Tory Ayers, his sister-in-law, who lived down the hall.

She questioned Elena again and said she did not have childcare experience. The nanny said she loved kids and took care of her younger brother. 

She seemed to come with some motive as she started capturing the picture of Ward's house construction design.

She created good bonding with the neighbors and gathered information from them.  

She said her boyfriend Jasper's aunt would be a problem if she joined as a nanny, as they planned to find old money in the building. 

Then the bond between Elena and Jesper started, and she took him to play in the park. She met two girls, Kim and Alex, who knew a little secret about the place. 

After the party, she starts checking around Tory's house while her drunk husband, Dick Aryes, finds out about it.

His daughter stepped into the room while he was making a deal.

Jocelyn came to Elena and gave a warning about Mattew and asked her not to trust him, although they treated her like a family.

Afterward, she met her partner at a cafe and gave him a blueprint of the building and basement.

They planned to steal the hidden treasure. Even Ms. Ivey lies to let her be a nanny and asks her to watch the Wards family. 

At last, Sylvie and Rex's nanny Ginny came with another twist when Elena learned there was no new girl in their quarter except them. 

She bonded with other nannies and discovered the previous nanny had disappeared without warning.

As a result, she started finding the truth. She even found the secret room while she snooped around Troy's apartment. In the last season, Ginny finds out about Elena's identity. 

Fans thought it was an interesting series. On Rotten Tomatoes, the series received an audience score of 67% and an average rating of 3.6 based on 12 users. 

Some viewers felt the plot is confusing. Although it is not in the Hitchcock style, it has an excellent story.

Even they said Kelly Bishop and Amy Acker had given an excellent job on the series with their astonishing act.

Fans said it's their favorite new show and especially liked Jon Eindhoven.

Viewers even shared their queries about the ruby as they didn't understand why they would hide something valuable at their house instead of a bank or safety deposit box.

Some viewers share a different reaction to the series, as they said the show got marketed as developed on the theme of Alfred Hitchcock style.

However, it was laughable to them as not close to being a Hitchcock-type show.