Echoes in Time by Andre Norton

Having revitalized the classic" Solar Queen" series to critical acclaim, Andre Norton and Sherwood Smith now turn their storytelling talents to Norton's popular "Time Traders" series.
Time agents Ross Murdock and Eveleen Riorden are recalled from their honeymoon to take part in a dangerous assignment: find a team of Russian scientists who have vanished without a trace from a research mission in the past of a far-off planet. Along with a team of Russian time Agents with their own mysterious agenda and Saba, a new agent teamed with Gordon Ashe, they leap into the alien world's distant history.
There they encounter several alien races, whose appearance, language, and customs are almost incomprehensibly strange. Something changed this world, and music seems the only tool that might prove a key to unlocking the planet's secrets.
But as they try to decipher a digital alien Rosetta stone, time is running out for their mission. Ross now knows what happened to the missing scientists--but can he save his team before they too vanish forever?
This thrilling adventure of a desperate race against treacherous time itself is a tale filled with excitement and wonder in the grand "Time Traders" tradition.

This book is part of the "Time Traders/Ross Murdock" series.
Here are some other books from this series: