From Publishers Weekly
Blending Arthurian legend and modern oceanography, Barron's (Heartlight; The Ancient One) lively tale boasts finely developed characters as well as fast-moving adventure. Thirteen-year-old Kate Gordon is assisting her father, an English-history professor, in his search for a sunken Spanish galleon off the Baja peninsula, when she rescues a whale that has gotten tangled in the expedition's equipment. That event propels the group into a quest for Merlin's legendary horn of power, hidden in the galleon, which in turn is surrounded by a huge whirlpool. After plunging into the whirlpool, Kate and her companions engage in an epic battle with Merlin's mortal enemy Nimue and her cadre of sea demons, who want to use the horn to extend their evil domain. Barron achieves a solid balance of mythology, environmental issues and scientific research procedures. The monsters are appropriately scary and malevolent, while the relationships among Kate, her father and the other members of the expedition are well drawn and touching. Ages 10-14. Copyright 1994 Reed Business Information, Inc.


From School Library Journal
Grade 6-8-Singing whales, a sunken Spanish galleon, genetics, and Arthurian characters are all jumbled together in this complex fantasy. Kate Gordon, 13, whose previous adventures (Heartlight [1990] and The Ancient One [1992, both Philomel]) involved her in both time and space travel, here accompanies her historian father to the coast of Baja, California, where he hopes to discover one of Merlin's legendary lost treasures. The quest leads Kate to the center of a whirlpool, to the place beyond it, and in the end results in her saving the lives of her father and his coworkers. While Barron's writing style is neither as smooth nor his characters as well developed as those found in novels by Lloyd Alexander, Ursula LeGuin, or Madeleine L'Engle, the plot moves swiftly and background information is generally well integrated into the story. Fans of adventure films, particularly Indiana Jones and the Last Crusade, will enjoy the intriguing mixture of contemporary life, historical detail, science, myth, and magic. While this title can be read independently, it will likely appeal most to readers already familiar with Barron's previous books. Fantasy buffs searching for fleshed-out characterizations, strong heroines, and a touch of humor would do well to check out titles by Tamora Pierce and Patricia Wrede, in addition to the classic works by the authors mentioned above.Lisa Dennis, The Carnegie Library of PittsburghCopyright 1994 Reed Business Information, Inc.


From Library Journal
While pursuing rumors of a lost Spanish galleon and a mysterious-possibly magical-drinking horn connected with Arthurian lore, a historian and his teenage daughter are drawn into an undersea world where they witness the final confrontation between a pair of legendary enemies. The author of The Ancient One (Putnam, 1992) blends a wealth of sea lore with ancient myth and fast-paced adventure suitable for adult and YA fantasy lovers.Copyright 1994 Reed Business Information, Inc.


From Booklist
Gr. 6-9. If 13-year-old Kate Gordon is the same 13-year-old


From Kirkus Reviews
The Merlin effect is a kind of immortality bestowed by Serilliant, a shell-shaped horn fashioned by the craftsman Emrys as a gift for his mermaid bride, Wintonwy. Merwas, king of the mer-people and Wintonwy's father, placed a rainbow colored liquid into Serilliant that would hold the power of eternal life--for those who understood it. Serilliant came into the wizard Merlin's hands and, because of his arrogance (he even renamed Serilliant ``the Horn of Merlin''), Merlin lost it. But all that was over a thousand years ago. Presently, Kate Gordon, 13, is spending the summer with her father, who is doing research in Baja California. Jim Gordon is a historian specializing in Merlin, and he has reason to believe that the Horn of Merlin is buried with a sunken ship, the Resurreccion, just off the coast. The problem is that he can't prove it because an enormous whirlpool makes getting close impossible. Well, not quite impossible: Kate is sucked into the whirlpool during a storm and finds the Resurreccion, Serilliant, and even Merlin himself. She participates in a sorcery-filled adventure, saves Serilliant, and proves her worth by returning it to its rightful place. No matter how you slice them, Arthurian legends are magical. T.A. Barron (The Ancient One, 1992, etc.) may not be in T.H. White's league, but he'll do. (Fiction. 10-14) -- Copyright ©1994, Kirkus Associates, LP. All rights reserved.


Midwest Book Review
Kate's journey to a remote lagoon to search for the roots of the King Arthur legend introduce her to more than shipwrecks: her rescue of a trapped whale involves her in an increasingly bizarre series of events which ultimately lead to a confrontation with Merlin himself. L'Engle's influence is highly evident throughout but enough originality shines through to make this more than a L'Engle clone.


Review
"Here is a story to celebrate! Readers young and old will savor this tale." -- Madeleine L'Engle

"Blending Arthurian legend and modern oceonography, Barron's lively tale boasts finely developed characters as well as fast-moving adventure....Well drawn and touching" --Publishers Weekly

"Another remarkable achievement" - Natalie Babbitt



Review
"Here is a story to celebrate! Readers young and old will savor this tale." -- Madeleine L'Engle

"Blending Arthurian legend and modern oceonography, Barron's lively tale boasts finely developed characters as well as fast-moving adventure....Well drawn and touching" --Publishers Weekly

"Another remarkable achievement" - Natalie Babbitt



Rocky Mountain News-09/94
Barron so successfully blends reality with fantasy that readers will find little difficulty in suspending their disbelief. Although Kate is a well-drawn personage, other human characters seem merely one-dimensional backdrops to the action. The strongly affirmative tone and the rapid momentum of the plot give this book universal appeal transcending all age barriers.


Lloyd Alexander-10/94
Tom Barron keeps adding exciting dimensions of creativity and imagination to his work. Here in The Merlin Effect, he explores fascinating new profundities, literally and figuratively; and his admirable Kate undergoes a remarkable sea change. The adventure becomes all the richer through its combination of Arthurian myth, genetics, and oceanography. As a result, the Heartlight Sequence gains still greater heart and brighter light.


Chinaberry Book Review-10/94
T.A. Barron has written yet another wonderful fantasy novel....A delightful, exceptionally compelling story with the depth and mythic quality we have come to expect from his writing.


Madeleine L'Engle-09/94
Here is a story to celebrate! Like the heroine, I was instantly pulled under the waves and swallowed by a great whirlpool. Like the heroine, I discovered that the power to chose--and, yes, to create--lies within us all. Readers young and old will savor this tale.


Review
"Here is a story to celebrate! Readers young and old will savor this tale." -- Madeleine L'Engle

"Blending Arthurian legend and modern oceonography, Barron's lively tale boasts finely developed characters as well as fast-moving adventure....Well drawn and touching" --Publishers Weekly

"Another remarkable achievement" - Natalie Babbitt



Book Description
Kate Gordon has traveled all the way to San Lazaro in Baja California ot help her fathr locate the sunken remains of the Resurrection--a galleon wrecked in 1547 and believed to cradle in its belly a fortune in gold and silver. But as Kate is about to discover, there lays entombed in the dark and treacherous waters of San Lazaro a treasure far more valuable than anything Kate could ever imagined: a magical drinking horn from Arthurian times wihch--as legend would have it--led to the demise of the great wizard Merlin.

Drawn by the power of the horn into an undersea world inhabited by strange and terrifying cratures, Kate must battle ancient forces to save her father's life...and her own.



Card catalog description
When she joins her father and several others investigating a strange whirlpool and possible sunken treasure ship off the coast of Baja California, thirteen-year-old Kate is drawn into a centuries-old conflict between Merlin and the evil Vagar.

ANNOTATION

When she joins her father and several others investigating a strange whirlpool and possible sunken treasure ship off the coast of Baja California, thirteen-year-old Kate is drawn into a centuries-old conflict between Merlin and the evil Vagar.

FROM THE PUBLISHER

Kate Gordon accompanies her father on a quest for a sunken Spanish galleon that contains a treasure beyond price—a mysterious drinking horn which legend states may have been responsible for Merlin's death. Now, to save her father's life, Kate must enter an undersea world of bizarre creatures and terrifying foes, and succeed where Merlin failed.

FROM THE CRITICS

Publishers Weekly

Blending Arthurian legend and modern oceanography, Barron's (Heartlight; The Ancient One) lively tale boasts finely developed characters as well as fast-moving adventure. Thirteen-year-old Kate Gordon is assisting her father, an English-history professor, in his search for a sunken Spanish galleon off the Baja peninsula, when she rescues a whale that has gotten tangled in the expedition's equipment. That event propels the group into a quest for Merlin's legendary horn of power, hidden in the galleon, which in turn is surrounded by a huge whirlpool. After plunging into the whirlpool, Kate and her companions engage in an epic battle with Merlin's mortal enemy Nimue and her cadre of sea demons, who want to use the horn to extend their evil domain. Barron achieves a solid balance of mythology, environmental issues and scientific research procedures. The monsters are appropriately scary and malevolent, while the relationships among Kate, her father and the other members of the expedition are well drawn and touching. Ages 10-14. (Sept.)

Library Journal

While pursuing rumors of a lost Spanish galleon and a mysterious-possibly magical-drinking horn connected with Arthurian lore, a historian and his teenage daughter are drawn into an undersea world where they witness the final confrontation between a pair of legendary enemies. The author of The Ancient One (Putnam, 1992) blends a wealth of sea lore with ancient myth and fast-paced adventure suitable for adult and YA fantasy lovers.

School Library Journal

Gr 6-8-Singing whales, a sunken Spanish galleon, genetics, and Arthurian characters are all jumbled together in this complex fantasy. Kate Gordon, 13, whose previous adventures (Heartlight [1990] and The Ancient One [1992, both Philomel]) involved her in both time and space travel, here accompanies her historian father to the coast of Baja, California, where he hopes to discover one of Merlin's legendary lost treasures. The quest leads Kate to the center of a whirlpool, to the place beyond it, and in the end results in her saving the lives of her father and his coworkers. While Barron's writing style is neither as smooth nor his characters as well developed as those found in novels by Lloyd Alexander, Ursula LeGuin, or Madeleine L'Engle, the plot moves swiftly and background information is generally well integrated into the story. Fans of adventure films, particularly Indiana Jones and the Last Crusade, will enjoy the intriguing mixture of contemporary life, historical detail, science, myth, and magic. While this title can be read independently, it will likely appeal most to readers already familiar with Barron's previous books. Fantasy buffs searching for fleshed-out characterizations, strong heroines, and a touch of humor would do well to check out titles by Tamora Pierce and Patricia Wrede, in addition to the classic works by the authors mentioned above.-Lisa Dennis, The Carnegie Library of Pittsburgh

BookList - Sally Estes

If 13-year-old Kate Gordon is the same 13-year-old Kate who is the protagonist in "Heartlight" (1990) and "The Ancient One" (1992), she is one busy teen, confronting and dispatching evil everywhere. In this companion to the other novels, she's at a remote lagoon in Baja California, where her father, one of the world's leading scholars on the legend of King Arthur, is searching for the lost Spanish galleon "Resurreccion" because research has led him to believe that the Horn of Merlin is aboard the ship. What ensues is a fast-paced adventure tale, both above and below the water, in which the ship turns out to be at the bottom of a mysterious whirlpool, and Kate and her dad become embroiled in the centuries-old struggle between the evil enchantress Nimue and the wizard Merlin for possession of the horn and its powers of immortality. Though characterizations lack dimension and the plot occasionally is too incredible, the story is steeped in Arthurian legend, which is the real draw here.

WHAT PEOPLE ARE SAYING

Here is a story to celebrate! Readers young and old will savor this tale. — Madeleine L'Engle