Time for Yesterday by A.C. Crispin (Star Trek #39, April 1988).

Admiral Kirk is summoned to the office of Admiral Morrow. Spock is there also. There is a problem. Waves of time have caught several stars, causing them to age suddenly. One has gone nova, others have started pouring out excess radiation giving signs of explosion or expansion into red giants. Several ships and inhabited planets are caught in the way, necessitating rescue operations. Dr. McCoy is on one of the affected ships.

But the cause is the troubling part. The Guardian of Forever, the time portal discovered by the Enterprise crew some years ago, is emanating the waves of time. The StarFleet personnel stationed on the planet do not respond, and must be presumed dead at this time. Since Kirk and crew are the ones who have dealt with the Guardian before, they are the logical team to tackle this project now.

Spock tells the admiral that there is one individual who has been able to directly influence the Guardian before: his son, Zar. But Zar is thousands of years in the past on the world Sarpeidon, the place of his birth and subsequent death. Kirk, Spock and McCoy had encountered him once before, when Romulans had tried to use the Guardian to change history and wipe out the Federation. Zar had been pulled back from the past then, and communicated telepathically with the sentient machine. Perhaps another powerful telepath could do the same.

D'berahan, a member of the telepathic Marishal race, is taken to the Guardian to attempt contact. But communicating with the powerful force of the Guardian shocks the small being, causing her to retreat into herself. Now, the only choice they have is to travel back in time to reach Zar. But Zar has troubles of his own, including an impending battle that may spell the end of his attempts to bring civilization to Sarpeidon.

And that only scratches the surface of the plot. Crispin went all-out with this story, checking in at just over 300 pages in paperback format. This book follows her first best-selling Star Trek novel, "Yesterday's Son" (Star Trek #11), the first paperback in the series to hit the best-seller lists. Both books act as sequels to the original series episode "All Our Yesterdays," when Kirk, Spock and McCoy inadvertently travelled into the past of the planet Sarpeidon, and Spock had an encounter with a woman named Zarabeth. That there was a physical relationship was never confirmed in the episode, but the possibility was left open. Crispin then posited the existence of a son.

The first book became popular largely due to the interest generated by the news of Spock having a son, reading about a Vulcan without Vulcan training, one with emotions. This was a Vulcan who could fall in love! It was especially popular with female fans.

This sequel is a better book, as Crispin by 1988 had become a better writer. The first book had been her first published novel. Now, she had written other tie-ins for franchises such as Star Wars and V, and begun working on her own series. This book reflects the added experience, and is simply bursting at the seams with plot.

There are a number of weaknesses here as well. The concentration is largely on Zar and secondarily Kirk, with a full helping of McCoy. The secondary characters are given some work to do, especially Uhura, but not a lot. The biggest part of the book is concerned with Zar's adventures as a tribal chieftain on a cold planet. Surrounded by enemies, he must gain whatever advantages he can by diplomacy before setting off for battle. And this must be settled before going to communicate with the Guardian. Crispin's characterizations of her own characters are fine, her Enterprise characters are a bit weak, especially Kirk, and Zar is still too strong a character. He can do too many things. It weakens the book.

The setting is just before the Star Trek II movie, and the cover uses the red uniforms from that time. Kirk is an admiral beginning to feel his age, McCoy is teaching, Spock is an Academy instructor, the rest are mostly teaching except for Chekov off on the Reliant. The crew is gathered for the mission by Admiral Morrow at Kirk's request, a theme that occurs often in the movies.

It's not a bad book, but it's not a great one. The overflowing of plot points may help you overlook the weaknesses.