The Enterprise is cruising the Mississippi when they come across a new bridge being built across the river near Rock Island. Disgusted that someone is trying to bypass the riverboats, Grey and Bill are happy to see that the work is going slowly.
Later, the Enterprise docks in St. Louis and railroad recruiter Jim Bledsoe arrives to try and recruit sailors as workers. Grey and Bill watch, disgusted, while Bledsoe offers passage money on top of wages. One river man complains that the railroad is cutting off their business but Bledsoe assures them that they can't stop progress. Meanwhile, Marie Maret returns to the Enterprise after shopping with her new husband, the much older Ferdinand. Grey goes to greet the attractive Frenchwoman and jokingly refers to Ferdinand as her father. She corrects him as Ferdinand arrives and gently complains that she's spending too much.
The river men on the dock attack Bledsoe, planning to hang him, and Grey fires a warning shot into the air to drive them off. Grey tells Bledsoe to leave and fast, but the recruiter books passage on the Enterprise. He's confident that Grey will continue blocking him, and the captain reluctantly takes Bledsoe on because they're short of passengers and need the fare.
The Enterprise heads out and Grey is forced to sail at night to keep on schedule. Bill comes to the pilothouse and complains about the night trip, but Grey points out that they have to compete against the railroad. Grey goes to his cabin but hears Bledsoe talking to the crew, looking for recruits. Bledsoe suggests that Carney could be a train engineer, but Carney isn't impressed. Grey breaks it up before the stoker can attack Bledsoe and tells the recruiter to stay away from the crew.
Bill spots a flatboat up ahead and pulls to a stop. Three drunken sailors are aboard and ask for a hogshead of pig tallow. Grey comes over and wonders why they need it, and their leader explains that they plan to burn down the rock Island railroad bridge. Disgusted, Grey refuses to help them just as Bledsoe runs up and tries to identify the men so he can report them to the authorities. Grey tells him to go back to his cabin and the recruiter punches Bill when he tries to stop him. The captain decks Bledsoe and the flatboat sailors cheer him on. However, Grey tells them to stay off his ship and insists that the only side he's on is the Enterprise.
Later, Grey goes down to the grand salon to play poker with Ferdinand and two other players. Marie plays the piano and Ferdinand talks about how he works as a lawyer in New Orleans. He loses and Grey tells him that he owes $150, and Ferdinand offers to cut for double or nothing. Marie tries to intervene but Ferdinand tells her to keep playing. He loses and Grey agrees to accept his IOU when the lawyer admits that he's short of money because of his wife's spending habits. Marie, upset, goes out onto the deck and Grey follows her out. She complains that Ferdinand treats her like a child and that she's not right for him, and Grey admits that it's strange how fate brings people together.
As Grey and Marie talk, the Enterprise suddenly slams into the Rock Island bridge. Grey runs to the pilothouse and meets Bill and Bledsoe. The recruiter complains that they deliberately rammed the bridge, and Grey has the crew take him away. Bill tells his partner that the current swept them into the bridge supports and that they'll need at least $400 to make repairs. Grey promises his partner that he'll sue the railroad to recover the money.
When the Enterprise arrives in Cairo, Grey has Grimes, the Rock Island Railroad Bridge representative, come aboard. Grimes has already talked to Bledsoe, who still believes that Bill rammed the bridge, and refuses to pay. Bill objects to the slur on his reputation and Grey argues that the bridge is a menace to navigation. Grimes assures him that they have experts who confirmed the bridge was safe, but Grey promises to sue for damages and halt the construction of any bridge across the Mississippi. Once the representative leaves, Bill wonders how they can afford a lawyer to present their case. Grey holds up the IOU and says that they have one.
Ferdinand accepts the case and they are soon in court. The bridge company has hired local lawyer Abraham Lincoln to represent them. Bill testifies first and Ferdinand has him describe his credentials. Lincoln interrupts to make a joke at Bill's expense, and the judge calls for honor when Carney and the others object. The young lawyer apologizes to the court and Ferdinand leads the witness. The judge overrules Lincoln's objection and Ferdinand keeps talking, thanking the judge until he finally tells Ferdinand to move on.
Ferdinand finally has Bill testify to the events that happened on the night of the collision. When Bill offers his opinion that the bridge doesn't belong there, Lincoln objects and the Judge sustains the objections. Ferdinand immediately wraps up at that point and assures Grey that he knows what he's doing. However, Grey isn't convinced. Lincoln cross-exams Bill and immediately concedes that the pilot is competent. However, he then asks Bill why he is typically in the wheelhouse during a trip. Bill reluctantly says that he's on duty when the river is tricky, and Lincoln asks why the pilot believed there was a danger at the time. The pilot finally admits that they were sailing at night despite the danger because they had to meet their schedule, and Lincoln dismisses him.
Later during a recess, Lincoln goes to the bridge and carves off wood shavings to measure the current speed. He then asks a young boy fishing off the bridge to help him in return for a dime. The lawyer has the boy announce when a log on the river reaches two points so that he can time it.
Back in court, Lincoln calls Grey to the stand and asks if Grey and the other river men don't like him. Carney and the other Enterprise crew laugh until the judge orders them to remain silent. Lincoln asks about Grey's experience and the captain angrily insists that he knows everything about the river because his life and career depend on it. Lincoln calls him a fighting man and Ferdinand objects, but Grey tells his own lawyer to sit down and shut up. He then complains that the bridges are navigational hazards and no one has the right to interfere with the riverboats' right of passage.
Lincoln asks Grey about how he was playing blackjack that night and jokes that Grey won himself a lawyer, and Carney and the crew laugh at his jibe. The lawyer then tells Grey what he found out about the river and asserts that the Enterprise was too close to the Iowa side of the Mississippi. The river was at flood stage and running too fast, and when Bill slowed down because it was dark, he didn't have enough steam to fight the current.
At that point, Lincoln concedes that the Enterprise struck the bridge by accident and that Bill is not at fault. However, he then continues by saying that despite that, no one has the right to prevent future building of bridges. Lincoln asks for a recess and the judge agrees, and Grey warns the young lawyer that he's lost. However, Lincoln points out that while the bridge was built in the wrong place, it still should have been built. Once their opponent leaves, Ferdinand assures Grey that they've won but Grey isn't convinced.
Later, Lincoln calls Grey back to the stand and asks him if the riverboats have a monopoly on trade. When Lincoln points out that the railroads are spreading west and competing with the riverboats, Grey insists that he's defending the future of all the people who live on the river and what happens if the trade dries up. Lincoln dismisses Grey but the captain refuses to step down until the judge threatens him with contempt. Once grey leaves the stand, Lincoln says that he's finished and the judge says that they'll hear closing arguments after a fifteen-minute recess.
Grey complains that Ferdinand didn't object to Lincoln's question and the lawyer insists that there was nothing to object to. The captain turns to Marie, asking her if Ferdinand is as important as she says, and Ferdinand tells her to go to the hotel and get some sleep. Marie finally has enough and tells her husband that he talks too much. However, she's glad that she's finally found a weakness in him because now she can reach him as a wife should reach a husband. Ferdinand realizes how upset she is and excuses himself to take her back to the hotel. Grey tells Bill that at least someone on their side will get something out of the trial.
After the recess, a much improved Ferdinand makes his closing statement and points out that even Lincoln has conceded that the bridge is a safety hazard. Lincoln then gives his statement and jokingly points out that Ferdinand is a better man, but tells the jury that his legal position is just as weak. The lawyer promises the jury that the bridge company will correct the bridge's position, but that there is no reason for trains to stop at the river, unload their cargo, and transfer it to the other side. Lincoln insists that the trains are necessary for the sake of progress and points out that the riverboats can no more impede the construction of safe bridges than someone could on a city street.
While the jury goes into deliberations, Marie congratulates her husband. Grey, Bill, and Carney go to get drinks while they wait. A local worker figures that they've won and Carney takes offense, but Grey stops the stoker from attacking the worker. Bledsoe comes in and boasts that the railroad has won, and Grey tells him to get out. When Bledsoe keeps recruiting, Grey comes over and the recruiter punches him. Grey punches him back and Carney figures that it's a good sign that they'll win. Bill comes in and tells them that the jury has reached a verdict.
In the courtroom, Lincoln notices the bruise on Grey's chin and asks what happened. Grey tells him that the river men won as usual, and takes his seat. The jury foreman announces the verdict: they've found in favor of the defendant as far as a restraint on construction, but in favor of the plaintiff for damages.
Later, Grey and Bill are preparing the Enterprise for departure when Lincoln arrives and asks to book passage home. They welcome him to the Enterprise and Lincoln congratulates Grey on his dedication to the river. Bill promises that they won't stop trying to prevent the bridge, but Grey realizes that they've lost. He warns Lincoln that he hasn't made himself popular along the river, and the lawyer regretfully admits that progress always hurts someone.