Both Ms. Shearer and Mr. Montgomery are quite good as the young lovers. Ms. Shearer was already an experienced silent actress, and this was her third talking film; Mr. Montgomery came to film directly from the New York stage, and seems comfortable in what is for Hollywood a new medium. He and Ms. Shearer would eventually appear in five films together (this was their first). Their acting (and that of Lewis Stone) is surprisingly subdued, given the film's proximity to the silent era. Ms Shearer would be nominated for an Oscar for her work as Lally, however she lost to herself in The Divorcee (TCM article).
Belle Bennett, however is still acting as though she is in a silent film - there is much emoting, much throwing her body around to convey emotions she has just spoken. As a result, the character of Harriet appears emotionally unstable. But Harriet is also written as being quite selfish. Certainly, she's had a hard blow with her husband's betrayal, but to force a promise from her young daughter to never marry and stay always with her is tantamountly unfair. Ms. Bennett had had a long career in silent films - her first was in 1913. Whether she would have ultimately made the transition to sound is unclear - she died of cancer in 1932, at the age of 41.
The part of Beth Cheevers is horribly underwritten. We have no clue as to why Hal would love her. At first, one wonders if she is a gold-digger, but as the story unfolds, we are informed that her former husband (whom she divorced to marry Hal) was quite well off financially. As written, Beth seems an unconcerned mother, a cold wife, and a nasty rival. All and all, Helene Millard is given little to work with, and nothing she does makes Beth relate-able.
Though based on a novel that was released the year before the film (AFI catalog), the script leaves something to be desired. Some plot aspects are problematic, as if the writers don't seem to know whether to concentrate on our young lovers, or on their parents. There is a scene in which Hal and Beth go to the country club and are shunned by their former friends. It's one scene, and it goes nowhere. The audience is going to find it hard to sympathize with either of them, so it is unclear why time is taken up with it. This is, however, definitely a pre-code film - witness that our adulterers are never punished for their actions, and there is a suggestion that Lally and Jack spend a night of passion together.
While the script is no great shakes, and some of the acting is dated, the interactions between Ms. Shearer and Mr. Montgomery is certainly worth the short running time of the film. We'll leave you with this early scene, in which Lally and Jack share a dance.