Grimwood's impressive debut novel, Breakthrough (Ballantine, 1976), was heavily influenced by EC Comics, concluding its blend of science fiction, reincarnation and horror elements with a surprising and unpredictable twist ending. Cured of epilepsy by a breakthrough in medical technology, 26-year-old Elizabeth Austin has miniature electrodes implanted in her brain. She can control her seizures by pressing an external remote to activate the electrodes. Adjusting to a normal life, she is ready to patch up a troubled marriage and resume her abandoned career. However, as part of the implant operation, Elizabeth gave her consent for the insertion of extra electrodes, featuring experimental functions unknown to science. When one of those electrodes is stimulated, Elizabeth experiences memories which are not her own. She discovers the remote has given her the ability to eavesdrop on her previous life 200 years in the past, and she keeps this a secret from her doctor. Intrigued, she finds the earlier existence appealing and begins to spend more and more time there. Eventually, she discovers that the woman in the past is a murderer who is plotting to kill Elizabeth's husband in the present.

Although Breakthrough went out of print shortly after publication, author Gary Carden ranked it alongside books by Stephen King and Ray Bradbury:

To write this novel, Grimwood did extensive research into brain surgery and epilepsy. Film producer William Castle took an interest in adapting Breakthrough for a movie, but the project was never realized. Breakthrough has certain parallels with David Williams' Second Sight (Simon and Schuster, 1977), coincidentally written the same year and later adapted for the TV movie, The Two Worlds of Jennie Logan (1979). Williams has commented, "As the author of Second Sight, I have to tell you that until I read this Wikipedia page in 2004, I had never heard of Ken Grimwood or his novel Breakthrough."

Grimwood used the pseudonym Alan Cochran on his novel Two Plus Two (Doubleday, 1980), but in Replay he offered a clue to Two Plus Two's true author with a sequence in which the main character of Replay hides his identity by using the name Alan Cochran. Behind Doubleday's cover blurb, "A Terrifying Novel of Murder in a Swinging Social Club," the storyline follows two Los Angeles detectives investigating a trio of murders. Doubleday described the book with this summary:

The 1988 World Fantasy Award went to Grimwood for his novel Replay (Arbor House, 1987), the compelling account of 43-year-old radio journalist Jeff Winston, who dies and awakens back in 1963 in his 18-year-old body. He then begins to relive his life with intact memories of the previous 25 years. This happens repeatedly with different events in each cycle. The novel was a bestseller in Japan, and its time-loop concept has been referenced as a precursor of Harold Ramis' comedy-drama Groundhog Day (1993).

Critic Daniel D. Shade outlined the book's buried messages when he reviewed the novel in 2001:

The novel was a selection of the Literary Guild and the Doubleday Book Club, and it was included in several lists of recommended reading: Modern Fantasy: The Hundred Best Novels (1988), Aurel Guillemette's The Best in Science Fiction (1993), David Pringle's Ultimate Guide to Science Fiction (1995) and the Locus Reader's Poll: Best Science Fiction Novel (1988). In the Locus 1998 poll of the best fantasy novels published prior to 1990, Replay placed #32. On the Internet Top 100 SF/Fantasy List, Replay was voted to the #43 position in 2000 but climbed to #19 by 2003.

In 1986, the agent Irene Webb sold the film rights to Replay to United Artists for a $100,000 option against a $400,000 purchase.

Grimwood's fascination with cetacean intelligence, encounters with dolphins and research into intraspecies dolphin communication gave him the inspiration for Into the Deep (William Morrow, 1995), about a marine biologist struggling to crack the code of dolphin intelligence. It features lengthy imaginative passages written from the point-of-view of several dolphin characters. To research "the willful denial and gratuitous cruelty" involved in tuna fishing, Grimwood secretly infiltrated the crew of a San Diego-based tuna boat. The publisher described the book:

Grimwood's environmental concerns were also evident in a letter he wrote to Los Angeles Times in 2002:

August 31, 2002, Saturday

Getting Those Nasty Butts Off the Streets

As an ex-smoker, I am also disgusted by the idea of thousands of cigarette butts littering the streets and ultimately being swept into the ocean ("Litterbugs and Butts," letter, Aug. 26). I am confused, however, about what smokers in largely pedestrian areas such as Westwood, Venice, the promenades in Santa Monica and Pasadena, and State Street in Santa Barbara are supposed to do with their smoldering butts.

Your letter writer suggests putting them in trash cans. Just how many trash fires per block would he like to see on an average day?

On a recent trip to Sydney, Australia, I noticed that the city has placed hotel-style ashtrays filled with sand on sidewalks throughout the central business district and the historic area called "the Rocks." Smokers obviously use them; I almost never saw cigarette butts crushed out on the streets or sidewalks in this delightfully clean and friendly city.

I know it may smack of "enabling" to rabidly anti-smoking Californians, but if we really want to keep the streets clean of this noxious litter, it might be a good idea to give smokers (including many foreign tourists) a safe and handy place to dispose of their used cigarettes.

Ken Grimwood

Santa Barbara

Other novels include The Voice Outside (1982), exploring mind control and telepathy-inducing drugs, and Elise (1979). Born in Versailles in 1683, Elise is immortal due to her DNA, and the story traces her experiences with various lovers and husbands through the centuries. Elise is now regarded as a rare book and sells at collector prices.

At age 59, Grimwood died of a heart attack in his home in Santa Barbara, California. At the time of his death, he was writing a sequel to Replay. He is included in the Guide to Santa Barbara Authors and Publishers at the University of California, Santa Barbara. There is at least one unpublished Grimwood novel, a collaboration with Tom Atwill.