A Detective at Death's Door — H.R.F. Keating

If Detective Harriet Martens's husband John hadn't been reading an Agatha Christie classic while the detective herself was sunning by the side of the club pool, she would have been dead before this story began. Unbeknownst to either of them, a killer had dropped a highly lethal addition into Harriet's cold drink. Struck by surprise to see the very symptoms of poisoning he'd been reading about, John was able to act---immediately!

Although he acted in time to save Harriet's life, she did not escape from the poisoning unscathed. She was bed-ridden for much too long a time before she was well enough to join in the search for her would-be murderer. But being imprisoned in bed gives one plenty of time to think, and Harriet soon realized that the attempt on her life was the initial move by an unknown who would soon earn the title of "serial killer." Even after there had been more murders, Harriet found it hard to convince her colleagues of this. They argued that the victims were too unrelated to each other; they did not know one another, had very different occupations, were widely apart socially and economically, and lived in neighborhoods scattered about the environs of the town. Except for the fact that they were English citizens, they had nothing in common.

Or---correction! They had nothing in common that Harriet's fellow police officers could see. But no one can say that Harriet is not tenacious. Once she is able to go about in person, if a bit shakily, she comes up with some helpful ideas. All the while, in the back of her mind, she knows that the killer, ego bruised, must be aching to finish what he or she started.