Ronnie Winslow is fourteen years old and is a cadet at the Royal Naval College. He is accused of stealing a five-shilling postal order, a financial piece of paper intended for sending money back and forth through the mail. There is an internal investigation, but Ronnie's family are never told about it, and so he does not have an attorney representing him. It is no surprise, then that the military investigators find him guilty as charged. Ronnie's father, Arthur, is asked to remove his son from the college but Arthur believes Ronnie when he tells him that he did not steal anything. Ronnie's sister Catherine doesn't believe the accusations either; she is a suffragette and always eager to represent those she feels to have been under-represented. With the assistance of their family solicitor, Desmond Curry, they begin an investigation of their own.
Their objective is to clear Ronnie's name - and to clear the family's name as well. This is all but impossible because under English law, military decisions were classed as acts of government. The government cannot be sued unless it gives its consent which entailed the Attorney General reviewing a petition of right, which traditionally was designed to enable individual citizens to get their property back from the Crown. Ronnie's case is the first in which the belonging that he wanted back was his good name.
The Winslows manage to engage a high profile and well-respected barrister, which is an attorney who specializes in courtroom trials and litigation. The barrister in question is Sir Robert Morton, who is also a hard-nosed politician. Catherine believes he will take the case on to prove some kind of political, partisan point, but to her surprise, he decides to represent Ronnie because he believes him, and because when he began questioning him in a mock cross-examination, he held up rather well. Morton believes he will hold up well in court as well.
Not surprisingly, the government does not want the case to go ahead. The reason they give for this is that it will distract from important Navy business, but thanks to Ronnie's family, who have been publicizing the case, Ronnie now has a great deal of public sympathy. Morton also gives a speech in Parliament which is so passionate and heartfelt that just as it seems they will be defeated, the Government gives in to public pressure and they are allowed to take the case to court.
The trial is difficult, and Morton and Curry work together to represent Ronnie, discrediting most of the Government's evidence against him, and embarrassing them publicly. The Admiralty are humiliated and also not convinced anymore that they got the right cadet. They withdraw all the charges against him, and he is declared innocent of the theft. His good name is restored.
However, the pressure and stress of the case has taken a toll on the family. Almost all of the family's money has been spent on the trial. Ronnie's older brother, Dickie, who is studying at Oxford, no longer has the money to continue. Catherine, engaged to John Watherstone, finds herself suddenlty dumped; John's father is a military man through and through and does not want him to marry into a family whom he feels has brought nothing but trouble to the Navy. Catherine considers marrying Desmond. She doesn't love him, but knows that he loves her, and marriage to him would at least provide some security. Ronnie's father's health has suffered a great deal too.
When Catherine learns that Morton was offered the appointment of Lord Chief Justice in return from dropping Ronnie's case, and that he turned the offer down flat, she wonders if she has mis-judged him all along - a judgement based primarily on his opposition to woman's suffrage, the issue closest to her heart. The play ends with a teasing suggestion to the audience that a romance is beginning to bloom between them.
