Cam Jansen and the Mystery of the UFO by David A. Adler, 1980.

Cam Jansen‘s friend, Eric, wants to enter a photography contest.  All of the pictures for the contest must be taken in black-and-white, have to be “of local interest”, and must be completely natural, not posed.  As Cam and Eric look for things to photograph, Cam spots a kitten trapped in a tree.  Eric takes a picture of her rescuing the kitten.

Then, they see a bunch of people standing around, pointing at some strange, multi-colored lights in the sky.  A local newscaster even shows up to cover the mysterious lights and talk about UFOs.

Cam and Eric decide to investigate the area where it look like the UFOs landed.  When they get there, they spot some strange creatures with silvery skin and pointed heads!  However, it soon becomes obvious that these “aliens” aren’t what they appear to be.  They speak English, are called “Cindy” and “Steven”, and are actually covered in aluminum foil.  But, why are they playing alien, and what are the UFOs really about?

Cam decides to keep the cat that she rescued and names her Neptune.  When the true purpose behind the aliens’ hoax is revealed, Neptune helps to foil their plans.