How do you catch a murderer without knowing who the victim is? Science-obsessed Grace?s fresh start with her dad in Devon is derailed when the smart speaker in their new house comes alive at midnight and says: I?m going to murder you. And after Grace begins to investigate, she uncovers four mysterious deaths ? all supposedly accidents ? that are linked to the device. But only Grace knows that one of those deaths was actually a murder ? and now she must identify both the victim and the killer, using the methodology of a chemistry experiment ? before she ends up dead herself.