Identifying a particular science fiction novel

Question

I'm trying to identify a science fiction novel I've read in my teens. Unfortunately, I don't remember a lot about it. Here's what I remember:

• It was hard science fiction.
• It featured space travel.
• It had an overt mystery / suspense tone, with an idea of larger / alien force at work.
• It featured a man, who (I believe) went on a space journey, and is coming back to Earth with a horrible realisation of something he has found (which, as far as I remember, isn't spelled out completely).
• I remember a particular scene where the narrator (who is also the man) speaks about his (former) life on Earth, describing his home with ocean view in San Francisco (or otherwise a coastal area of California, but it could have been the east coast too).
• I read it during the late 90s, roughly 1995-2000.
• The cover art mostly had blue colours, with some kind of space vessel (in black or otherwise dark colours) depicted on it.

I'm sorry this sounds all very vague, but I don't remember much further. Does it ring a bell to anyone?

Edit: at the request of some, I'm adding here other random bits for the correctness of which I wouldn't vouch and which could be completely wrong or unrelated to the novel. While I'm relatively certain about the above, the following should be taken with a grain of salt:

• I believe that the novel also came out during that time period, as I bought it at a local book store browsing along (then) contemporary science fiction works.
• I believe that the narrator is writing to a female, possiblity his lover, who is expecting his return. I.e. there is some relationship/romanic side, though it is not the major point of the story. Probably just a means to tell the story.
• I (think I) remember vaguely that the discovery the narrator made was related to him being manipulated in some way (genetically or otherwise mentally) by the aforementioned higher force. It is possible that on the ship he's returning on, he's carrying along that force in some way. While there was no explicit 'end of the world' / 'destruction of humanity' theme, it is hinted that the man returning home is not in any way the man who set out on the journey.
• In the scene where the beach house is mentioned, I believe the ocean is compared to the vastness of the universe in quite a dark tone.
• Exploration might have been the reason the man went into space. He flew alone, at speeds faster than light, and the journey was long, lasting a few light years at the least.

Again, I might be confusing all of these with odd bits from other science fiction works. For the record, I'm mostly a fantasy reader (Wheel of Time, The Seventh Gate) and have not read a lot of pure science fiction (bar a few collections of short stories from Nebula Award winners). You could contend I should remember it better, but as noted it's been a while and the strongest lingering memory I have from this story is this ominous feeling of discovering something horrible about the universe.

Edit 2: added a few unconfirmed points resulting from answers to questions posed here. I will continue to update the entry as I add answers and note this at the bottom in case you've already read the original question.

Answer 1

Parts of it sounds like the short story "Bordered in Black" by Larry Niven. It is in a collection of his work, called Inconstant Moon and has a spaceship on a blue cover.

Synopsis

A prototype faster-than-light spacecraft crewed by two men is sent to the Sirius system, known from robotic exploration to include an earthlike world. In orbit around the world, they notice that one of the continents has a thin, strange border all the way round its coastline, which radiates a low heat and appears black in visible light. After exploring the edges of the smaller continents, and discovering that the ocean hosts only one lifeform—a single species of algae that they think might have been genetically engineered—they decide to explore the large continent with the border.

When they discover just what the black border is—a seething mass of trapped humans with very dark skin, feeding off the algae and each other—the result is the death, by suicide, of one of the crew, and the self-destruction of the ship by the traumatized survivor upon his return to Earth—and a chilling reminder that there may be great danger waiting for further human explorers. The story ends on a hopeful note, with the project leader believing that Earth can help the humans at Sirius, and a fearful one, with the crewman then speculating that the humans were seeded by carnivorous aliens as food animals.

• It was hard science fiction.

  Fits with the story/author

• It featured space travel.

  Check.

• It had an overt mystery / suspense tone, with an idea of larger / alien force at work.

  Narrator suggests the planet they visited was a farm planet, and that the humanoids had been put there as a food source by aliens.

• It featured a man, who (I believe) went on a space journey, and is coming back to Earth with a horrible realisation of something he has found (which, as far as I remember, isn't spelled out completely).

  As above. Narrator is the survivor of the two man crew. Realisation is that the universe is a dangerous place.

• I remember a particular scene where the narrator (who is also the man) speaks about his (former) life on Earth, describing his home with ocean view in San Francisco (or otherwise a coastal area of California, but it could have been the east coast too).

  This doesn't fit.

• I read it during the late 90s, roughly 1995-2000.

  Inconstant Moon was first published in 1973, but the edition with the blue cover is from Sphere and was published in 1988.

• The cover art mostly had blue colours, with some kind of space vessel (in black or otherwise dark colours) depicted on it.

  See above.

Most of the other points don't fit, but the next one does:

• Exploration might have been the reason the man went into space. He flew alone, at speeds faster than light, and the journey was long, lasting a few light years at the least.

  The spaceship (OverCee) was the first of its kind. The journey back (after his co-pilot was killed/killed himself) is particularly long.

Answer 2

This is a very long shot. But perhaps Ben Bova's Voyagers series which started in 1981 but later books were published in the later 80s and 90s?

In particular the part about an man returning from space with an unknown secret of some kind matches somewhat to what the protagonist Keith Stoner does. Too, there is a love relationship that occurs within the storyline. I am pretty sure he was located in California (Pasadena JPL? if I remember correctly)

Though, many of the other particulars don't match, so this is iffy at best. In particular, this is not written in first person that I remembers.

However below are some book covers which also seem to resemble your description. Do any of these ring a bell?

Good luck.

Answer 3

Maybe the three stigmata of Palmer Eldritch, it has some features in common, but not that many.

• It was hard science fiction. -Sort of
• It featured space travel. -yes
• It had an overt mystery / suspense tone, with an idea of larger / alien force at work. - mostly yes
• It featured a man, who (I believe) went on a space journey, and is coming back to Earth with a horrible realisation of something he has found (which, as far as I remember, isn't spelled out completely).- Yes
• I remember a particular scene where the narrator (who is also the man) speaks about his (former) life on Earth, describing his home with ocean view in San Francisco (or otherwise a coastal area of California, but it could have been the east coast too).- Don't think so
• I read it during the late 90s, roughly 1995-2000.- no, it's from 1965, but had several reeditions
• The cover art mostly had blue colours, with some kind of space vessel (in black or otherwise dark colours) depicted on it.- Yes in some of the covers