When Tom meets Isabel (Alicia Vikander) in the mainland town where she grew up, their instant attraction is almost overwhelming. They marry, and he takes her to Janus Rock, where they live in isolated bliss until she miscarries. A second miscarriage occurs while he is tending the lighthouse during a furious storm and leaves them feeling desolate.  Mr. Fassbender and Ms. Vikander make one of the most compelling pairs of screen lovers in the grand David O. Selznick tradition that I’ve come across in many years. Unlike so many contemporary movie stars, both actors convey a remarkable depth and range of feeling. With that goes an awareness of the essential unknowability of a partner in a relationship, even one as passionate as theirs.  At his most besotted, Tom still keeps something of himself in reserve. Behind his icy, imperious gaze, you can discern the pain of the past, along with a certain inviolable nobility of spirit. Here and in earlier films, Mr. Fassbender’s screen persona suggests a dashing but harder-edged answer to the Daniel Day-Lewis of “The Age of Innocence.” Ms. Vikander mostly keeps in check the tempestuous, fiery side of Isabel, whom you sense, even at the beginning, to be on the verge of eruption. From the moment the two meet, she regards him with a desire that registers as an unflinching determination.  The Times critic Stephen Holden reviews “The Light Between Oceans.”  Their inspired pairing suggests that Mr. Cianfrance is a true believer in the romantic imagination: a mystique eroded by social and technological forces that have broken down traditional restraints against intimacy and privacy so that little mystery is left. The last remnant of the romantic imagination is its cheap first cousin, the erotic imagination.  “The Light Between Oceans” begins to lose its majesty when a dinghy appears on the shore. It contains a baby girl and the dead body of a man who is apparently her father. Tom insists they report the child to the authorities, while Isabel, still grieving, begs him to remain silent, allowing them to keep the baby and raise her as their own.  At this point in “The Light Between Oceans,” the pounding surf turns into soapsuds and the brine into tears. Several years later, on a trip to Isabel’s hometown, they meet Hannah (Rachel Weisz), a mournful woman who lost her husband and their baby girl at sea around the time the dinghy washed ashore. Realizing that the lost child is the baby they rescued, Tom, feeling guilty, furtively breaches his vow of secrecy with Isabel and drops enough hints to spur an investigation and a bitter struggle between Isabel and Hannah for possession of the child.  “The Light Between Oceans” begins to suggest an overly plotted, high-end Nicholas Sparks film awash in tears, pleas and threats, and acts of treachery and nobility. Where Mr. Fassbender’s sorrowful gravity anchored the movie’s first half, Ms. Vikander’s volatility sparks the second half with Ms. Weisz’s aggrieved, conflicted Hannah providing a moral fulcrum.  Remaining true to the novel, “The Light Between Oceans” steadily becomes a strained fable about forgiveness and revenge that sabotages its best intentions by taking one too many plot turns. But unlike a movie spun off from a novel by Mr. Sparks, the story still remains weightier than mechanical literary claptrap. It eventually dribbles away in a final, perfunctory flash-forward that feels hastily tacked on, even though it’s in the novel.  As a drama about adult responsibility, selfishness and moral obligations, however, it never wavers in its commitment to examine what it means to raise a child.  “The Light Between Oceans” is rated PG-13 (Parents strongly cautioned) for thematic content and sexual situations. Running time: 2 hours 12 minutes.  Writers Derek Cianfrance, M.L. Stedman  Stars Michael Fassbender, Alicia Vikander, Rachel Weisz, Florence Clery  A version of this review appears in print on September 2, 2016, on page C1 of the New York edition with the headline: Oh, Look, There’s a Baby in a Boat. Order Reprints| Today's Paper|Subscribe
Michael Fassbender and Alicia Vikander play an Australian couple who long for a child — and happen to find one — in this post-World War I romance.