From audible.com:

The first original novel tying into the critically acclaimed and much-missed Firefly series from creator Joss Whedon

The Battle of Serenity Valley was the turning point that led the Independents to their defeat at the hands of the Alliance. Yet the Browncoats had held the valley for weeks against all odds, before being ordered to lay down their arms. Command stated they refused to send in airpower because the ground war was "too hot". But the soldiers who were there insist that was not true....

While picking up a new cargo on Persephone, Captain Malcolm Reynolds is kidnapped by a bunch of embittered veteran Browncoats who suspect him of sabotaging the Independents during the war. As the rest of the crew struggle to locate him, Mal is placed on trial for his life, fighting compelling evidence that someone did indeed betray them to the Alliance all those years ago. As old comrades and old rivals crawl out of the woodwork, Mal must prove his innocence, but his captors are desperate and destitute, and will settle for nothing less than the culprit’s blood.

From audible.com:

Mal and the crew take receipt of a sealed crate that they are being paid to transport to Badger, no questions asked. Yet once their cargo is safely stowed aboard, River insists Mal should "space" it out of the airlock, for it contains, she insists, ghosts.

With supplies running low, the crew desperately needs another payday but soon finds itself paralyzed by hallucinations of their deepest hopes and desires, so vivid they cannot be distinguished from reality. River is the only one unaffected. She desperately tries to awaken her crew mates, while the fantasies turn sour and the ship begins to spin out of control.

From audible.com:

The fifth original novel from the much-loved space western Firefly, produced with Joss Whedon as consulting editor, set between the TV series and the movie Serenity.

Deadly disease

Months after Inara leaves Serenity, Mal and the crew finally learn the reason for her sudden departure: She is dying of a terminal illness. It is Kiehl’s Myeloma, a form of cancer that’s supposedly incurable, and Inara has very little time left.

A disreputable scientist

Through their shock and despair, rumors of a cure reach the crew. Expert Esau Weng is said to have developed a means to treat Inara’s condition, but he has been disgraced and incarcerated for life on a notorious Alliance prison planet.

An infamous prison

On Atata planet, inmates are abandoned with no guards and left to survive as best they can. What’s more, terraforming the planet did not take properly, so the world is a frozen wasteland. To save Inara, the Serenity crew must infiltrate the prison....

From audible.com:

The second original novel from the much-missed Space Western Firefly, produced with Joss Whedon as consulting editor, set between the TV series and the movie Serenity

A cosmic cry for help

Captain Mal Reynolds is in a fix. He’d like nothing more than to find honest smuggling work that stays under the Alliance’s radar and keeps the good ship Serenity in the sky. But when an old flame of Jayne Cobb’s sends a desperate plea across the galaxy, his crew has other ideas.

A cutthroat bandit

On the arid, far-flung world of Thetis, the terrifying Elias Vandal is threatening to overrun the town of Coogan’s Bluff with his trigger-happy army. He wants control of the only thing standing between its people and dustbowl ruin: their water supply.

The magnificent nine

When the crew land at the hardscrabble desert outpost, they discover two things: a savage outlaw gang who will stop at nothing to get what they want, and that Jayne’s former girlfriend, Temperance, is single-handedly raising a teenage daughter, born less than a year after she and Jayne parted ways. A daughter by the name of Jane McCloud....