He tags along with his big brother on a Mission of Fratricide (we slowly see that Big Brother is a fucking monster although he thinks he's reformed. They escape to a magic city under water, a reflection of their home, and Random is sentenced to a unique sentence for having seduced the Queen's daughter, knocking her up, and abandoning her. She proceeded to commit suicide; he proceeded to have no contact with his kid. Random claims he made no promises to the dead woman. Her mom is still pissed.
His big dire sentence that he faces with a cigarette and blindfold? He has to marry a pretty lady named Viallewho is even shorter than he is. They must remain married for one year, at which point he's free to go off and live his own life. The assumption is that a marriage and divorce to a powerful guy like Random will raise her social class. Somehow. Spoiler: she's blind.
She goes from a complete cipher with character traits like "is female" and "is blind" to a pretty interesting and powerful person with goals and motivations that don't center the men in her life.. She and Random fall in love, something that he never expected to happen ever from anyone.
This pretty much all happens off page, between the lines.
The Amber novels are 2 cycles, each narrated by different people. They're both pretty absorbed in their own interests and Random and Vialle are side characters. It's a big jump from "ugh I gotta marry this ugly bitch I GUESS maybe someone will kill her" to "I love her. I've never felt this way about anyone before. And she loves me. I didn't think that would happen. I didn't think that could happen." (that confession is interrupted by a big "I don't care" from the narrator, btw)
I think about the stuff that Zelazny doesn't say a lot. There's a lot going on just out of earshot, just around the corner. His writing can be really sparse, leaving the reader to draw a lot of conclusions and fill in a lot of blanks, a detective noir type writing style but involving gods and immortal beings and eternal college students who wrangle with aliens and guys on road trips trying to change history.
Random plays the drums, is a jazz musician. He loves flying. He does drugs. He's curious. He's cunning. He wants to be accepted, and loved, and hates being vulnerable so he lashes out. Of all the siblings he grows the most over the course of the books and he is a relatively minor character. Vialle is a sculptor who leaves her entire world behind to be with a man she'd only known a few months who failed his attempted combo fratricide/regicide. How did they go from strangers in an arranged marriage to frinds, to allies, to lovers?
That's not the story that Zelazny wanted to tell, so he didn't. But it's one that I want to know, so I'm telling it.