It is basically two overlapping stories. A computer scientist (Tessa) experimenting with artificial intelligence creates a program that starts to think like a person but an evil one at that. It invades the Internet and is able to get into any computer in the world. Tessa realizing the danger of the program, tries to combat it and is almost killed by it.
In the meantime the second story is happening in Los Angeles where a serial killer uses the Internet to "social engineer" information about his intended victims and then pose as lost relatives or other fake people associated with the victims.
Somehow Tessa's program becomes aware of the killer and starts to give him guidance and ultimately the program wants the killer to eliminate Tessa.
The book drags in parts and the way the AI program thinks and is able to take over the Internet is a little far-fetched. There are also parts of the book where you expect Tessa to form a relationship with an FBI agent that never happens.
A couple of themes from some of Ambrose's prior books (specifically Coincidence) appear here such as the thought that the whole world is a computer program running on a teenager's computer somewhere waiting to be shut off by the teenager's father.
Ambrose is a very talented writer and with a little honing he can probably make his next thriller a full 5 stars.
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