Born to a wealthy family whose fortune came from Cornish tin, Trevelyan manages his own companies under the umbrella of the East India Company. His position allows him to move in society with dukes and ministers and influence politics.
His father is a baronet, and has a brother in Parliament. Through his friendship to Harold Grey, he became engaged to Olivia Pearsall.
In June 1757, Joseph is unaware that while using the privy at The Society for the Appreciation of the English Beefsteak he is being watched by Lord John Grey, cousin of his betrothed Olivia Pearsall. He carries on with his evening dining with Lord Hanley and Mr. Pitt. Trevelyan remains unaware that Grey has taken up a personal investigation into him and the disease that afflicts him. He declines Grey’s offer to attend a brothel saying he swore to his mother upon her deathbed he’d never go to a whore.
During one of Benedicta Grey’s Wednesday parties Trevelyan and Grey bond a little over their dislike of Stephan von Namtzen. Trevelyan is outraged when Grey mentions Tom Byrd having come to him saying that he had sent him. Trevelyan wished to whip the boy and otherwise dismiss him from his employ. Grey tells him Tom has snuck off so the whipping could not take place but Trevelyan still held the mind that Tom was no longer in his employ.
Through various sources; Nessie, Rabbie MacNab, and Richard Caswell Grey learns about Trevelyan’s secret meetings at the Lavender House where he dresses in drag to keep his identity secret and meets with his lover. This and the murder of an unidentified man in a green velvet dress brings Grey to Trevelyan’s warehouse at the docks. Caught unaware Trevelyan is gracious and brings Grey to his office to discuss this private matter that had Grey concerned.
The news that Grey wishes his engagement to Olivia to be terminated was surprising though he doesn’t show signs of shock beyond blinking. When he inquires why Grey has chosen to take this rash step Grey reveals the bloodstained scrap of green velvet. He knew the garment, though tries to not let on excusing himself to ensure they are undisturbed. Trevelyan attempts to remain calm about things offering Grey some sherry and drinking to "the truth". Small things like a twitch of his eye and a tightening of his jaw give way that he is concerned how much Grey really knows. Trevelyan begins to react badly as Grey implies he has a connection to the dead "woman", Mr. Scanlon, and to Lavender House.
Trevelyan however takes Grey at a disadvantage as he points out that Sir John is currently in Bath and would therefore not have known or anything to do with this matter as Grey implied. To counter this Grey reveals that he is aware that Trevelyan is poxed and thus he forbids the marriage to take place.Trevelyan tries to turn it as Grey’s mistake and misguided delusion. Trevelyan going so far as offering a coach to take Grey to a Doctor who has a history of treating nervous disorders. Grey makes it clear that he is not insane and the engagement must end. Trevelyan asking for three days to find an adequate reason to give for the engagement being terminated that would not harm his nor Olivia’s reputations. Grey agrees giving him the time as he had wanted Trevelyan to find a way out of the engagement from the start.
Trevelyan plans to sail on his ship the Nampara with Maria. This plan was only slightly impeded by Grey’s sudden arrival in his cabin, the ship setting sail just the same. Grey notices Maria asleep, wearing Trevelyan’s ring loose upon her finger. Scanlon explains that Maria is currently suffering from Malaria. Trevelyan offers to give Grey the full truth over a drink. Grey refusing the drink not wishing to be poisoned again. Trevelyan admits he’d not planned to kill him just delay him, but would not have been put off if Grey had died. Trevelyan still denies that he has killed anyone.
Grey finds that Trevelyan is in possession of the papers O’Connell stole - openly admitting he got them from O’Connell. Trevelyan goes on to reveal that he married Maria on Tuesday, a look of great pride in his face. Trevelyan tells how he met Maria the May of 1756 and he fell instantly in love with her, despite knowing she was married and at the time mourning the loss of her child. Given her devout Catholic nature it had taken him several months of persistence before she yielded. Trevelyan went on referring to Reinhardt Mayrhofer as a degenerate, womanizer, and worse. He assures Grey this was all before his betrothal to Olivia, and since Maria would not leave her husband he agreed to marry Olivia intending to continue his affair with Maria. To ensure that Mayrhofer couldn’t blackmail him Trevelyan set out to investigate him and set him up, this leading Trevelyan to Hubert Bowles. Trevelyan going on to explain that he owns both Lavender House and Mags’ brothel.
Scanlon explains his involvement in the matter started with Jack saving Francie and placing Scanlon in his debt. Trevelyan explains that he believes O’Connell hadn’t returned for his wife but for a place to stash the papers will he could find a buyer. As the conversation continued Trevelyan explains he planned to use Mayrhofer as a patsy to set him and O’Connell up together and get his competition out of the way to further his pursuit of Maria. It was O’Connell mistaking that Trevelyan is Mayrhofer just using a fake name that led him to Lavender House only to find no such person.
O’Connell only finding the connection because Trevelyan had been in a rush to see Maria and not followed his normal meticulous routine. Both Trevelyan and Maria using the same green dress, the green only because it is his favorite color. Still trying to determine who murdered O’Connell and Mayrhofer a sickly Maria awakens and confesses to the murder of her husband. Knowing they were at sea she felt no issues with confessing. Maria mocking Grey when he said people knew where he was, pointing out their destination of India. Maria was confused by the name O’Connell not knowing who he was. All questioning came to a stop as Maria was overcome by a bout of malaria chills.
Trevelyan calls for Scanlon to tend to her telling Grey she cannot speak to him but he would. Maria pleads for Trevelyan to tell Grey as if they are both dead she will be justified. Trevelyan led the way up to the deck. Trevelyan stern in his conviction that Maria will not die. As they walk on the deck Grey is mindful of his footing wearing leather shoes - thinking about how he was unconvinced that Maria could have done the damaged inflicted upon her husband and then about how Olivia would be seen as a jilted fiancee but at least have her reputation intact.
Grey briefly thought if anyone would send words to the Byrd family as he looked up to the rigging and saw the brothers. Grey’s thoughts turned to his own fate, Harry’s, Hal’s and the regiment now that it was proven O’Connell was the spy and they’d not managed to stop him in time. Pulled from his thoughts as Trevelyan asked how he had come to know he was poxed. Grey was blunt in his reply telling him about seeing it at the privy in the Beefsteak. Trevelyan explains he became poxed via Maria - who was innocent in it all - as her whore-mongering husband was the one who’d given it to her. Maria had been unaware of her condition or that this condition caused her son to be malformed. Trevelyan tells Grey further that to avoid the burden of a malformed son and his wife learning the truth of why the child was malformed, smothered the infant the day after he was born.
Trevelyan had the doctor tell Maria all he’d told him, in hopes she’d leave the man finally. But instead she sent him away and held herself in her room for a week seeing only servants contemplating suicide. Trevelyan however refused to give up and sent Jack to Scanlon to learn what might be done for the affliction. It while Maria was alone in this depression that Mayrhofer admitted to killing their child, laughing as he did. Maria went into a fit of rage and threatened to reveal his affairs, his condition and that he is a murder publicly. Mayrhofer left her only to return wearing her green dress threatening to expose her own affair if she dare spoke against him. And it was at this that she used her pistol shooting him. Trevelyan confesses that he and Jack had smashed in the man’s face.
Trevelyan and his ever trusted and good servant Jack had taken the body dosing it with pig’s blood and taken the body to an area where if found it would be mistaken for a prostitute. The blood to cover the bullet wound and to stain the garment so no one would think to remove it. Well no one save Grey it appeared. Their talk came to an end as Jack came to fetch Trevelyan, Maria feeling better, and to say that Scanlon was in the mess ready to speak with Grey. There was something in the way Jack looked at Trevelyan that got Grey wondering just how close Jack and Trevelyan were, but dismissed the thought going to speak with Scanlon.
Scanlon explains to Grey that he infected Maria and Trevelyan with malaria as a cure for the pox - the fever burning out the syphilis. Trevelyan having waited till that day to take the cure. Grey summarizing that Trevelyan didn’t mean to run away and die with his lover but to overcome the disease they both suffered and live together.
Eight days pass and Maria’s condition had not improved. Trevelyan scarcely leaving her side. Scanlon putting on a good face saying she will recover. And Jack worried - though not for Maria but for Trevelyan. A ship is spotted and Grey hopes it might be a way back to England. Scalanon goes below to check with Trevelyan about possibly stopping to board the ship and sail back. As Grey hurries to get his letter to send back he slips hitting his head, waking to Jack watching over him. Grey becomes more aware that Jack harbors feelings for Trevelyan though Grey is uncertain if they are returned. From his own personal knowledge he tells Jack that no matter what Trevelyan will never forget or stop loving Maria - especially if she dies. Grey offers Jack a position at his mother’s home if he wished to return to London with he and Tom. The Scorpion, a troopship, has come alongside them and Tom rushes in to announce news from The Scorpion that they’d won Bengal.
On August 18,1757 Lord John Grey has returned to London and is attending a party at his mother’s home for the victory in Bengal. Jack had chosen to return with Grey and Tom, though at first was quit to the point of taciturnity. The festivities however, seeming to have a cheering effect as Grey noticed Jack smiling at a young maid. The public hysteria over the victory had eclipsed the other news and gossip. So no word had been spread about Mayrhofer, Trevelyan, or about his jilted fiancee Olivia. For this Grey is thankful. He reflects on the last time he saw Trevelyan, at the bedside of Maria. Trevelyan saying that word would eventually be sent he’d died at sea. Which if Maria dies would be true and he would carry her over the edge and and die with her. However, if she lived they would live out their life in India.
On May 9th, 1756 Joseph met Maria Mayrhofer at one of Lady Bracknell's salons. At the suggestion of their hostess, Joseph approached Maria after being told that this was her first social event since the death of her child. Joseph had fallen in love at first sight and without hesitation or thought greeted her with a kiss on the hand, said, "God Help me I'm in love with you," and she laughed saying, "God help me, then." Maria, being a devout, married Catholic, initially refused his attempts to woo her. After several months, however, she yielded to him and they began their affair.
Not knowing she was infected, Maria passed the syphilis she contracted from her husband to Trevelyan. Given that she was married and refused to leave her husband, Trevelyan agreed to be betrothed to Olivia Pearsall, and he undertook to continue his secret meetings with Maria with the utmost discretion, even utilizing the disguise of a molly in a green dress. They used Lavender House as a rendezvous point, arriving and departing separately all but one time, and using different chairmen each time.
After discovering his affliction, Trevelyan went to a doctor and discovered that Reinhardt was the source, as well as further horrific details about what happened to Maria's child. Hoping that this news would induce Maria to leave her husband, he asked the doctor to tell her exactly what he told him. Instead, Maria sent him away and shut herself in her chambers, refusing to see anyone and contemplating suicide. In an effort to help and protect her, Trevelyan had Jack Byrd watch over her and brought Finbar Scanlon to try and cure her syphilis by giving her malaria. The cure did work, but with the obvious consequence that Maria now suffered from severe malarial fevers.
After Maria had murdered her husband, Trevelyan and Jack beat his face in and doused him in pigs blood before dumping him in a location where, if found, he would be taken for a dead prostitute. In the wake of the death of her husband, Trevelyan marries Maria and flees with her, Jack, and Scanlon upon one of his ships to India. On board the ship, Trevelyan allows Scanlon to infect him with malaria to cure his syphilis, leaving the matter in God's hands whether the newlyweds should live happily ever after, or die together.
Joseph agreed to become betrothed to his good friend Harold Grey's cousin and ward Olivia Pearsall due to the fact that his lover Maria Mayrhofer refused to leave her husband. If he had thought there was a chance Maria would leave Reinhardt he would never have agreed to the marriage. The betrothal was of convince more than love and Trevelyan intended to not end his affair with Maria after marrying Olivia.
When Lord John Grey approached him insisting the betrothal be terminated due to Trevelyan being poxed Trevelyan requested three days to come up with a reasonable reason to call of the wedding that would save both him and Olivia face. The time he asked for was just for time to flee the country with his lover. Following the death of Reinhardt Trevelyan married Maria and took her away by sea to India. He explains to Lord John that word would come back that he had died at sea, this eliminating Olivia of being thought of as jilted by her fiancee and making her free to marry someone else of good standing.