Railroad bos Blayden (Edward Earle) is determined to build a tunnel
through Mystery Mountain, however, his efforts are constantly thwarted by
a masked and cloaked villain called the Rattler, who sabotages the
construction work and terrorizes the workers. Blayden suspects Corwin
(Lafe McKee) of the Corwin transportation comany to be the Rattler, out to
fight his competition - but then Corwin himself is murdered.
Desperate to find out who the Rattler is, Blayden asks for the
assistance of Ken Williams (Ken Maynard), railroad detective, who soon
arrives with his pal, klutzy reporter Breezy Baker (Syd Saylor).
Soon, everybody is under suspicion to be the Rattler, at least for a
while, including Corwin's daughter Jane (Verna Hillie), who continues her
father's work, local physician Dr Edwards (Hooper Atchley), who owns some
land on Mystery Mountain, telegrapher Mathews (Lynton Brent), and even Ken
Eventually though, quite a few shoot-outs and chases later, Breezy
stumbles over the Rattler's secret: The Rattler has a secret, large
goldmine in Mystery Mountain in question, and he's hell-bent to defend it.
Plus, he has a large collection of lifelike masks so he can impersonate
and throw suspicion onto pretty much anyone. But that leaves one question
open ... Who is the Rattler ?
Finally, Ken goes hand-on-hand with the Rattler, tears off his mask,
and it turns out to be ... Doc Edwards. But Edwards not only gets away, he
also beats up Ken's horse Tarzan. This gives Ken an idea: to ultimately
prove who the Rattler is, he uses Tarzan's animal instincts when he
gathers all the suspects and lets him pick the culprit. To everyone's
surprise, Tarzan does not pick Doc Edwards (the audience knows by now the
Rattler was wearing another of his masks), but suddenly, Blayden the
railroad boss makes a hasty getaway - and rides right into his own mine,
which he had rigged to blow up at a certain time ... and boom, there goes
the Rattler !
A typical, nevertheless highly effective Mascot serial: It
contains all the usual elements: a masked villain, a secret goldmine,
secret passageways, a convoluted murder mystery, and of course massive
fist fights, shoot outs and horse-riding. The Rattler's mask has to be one
of the silliest - it's simply sunglasses, a fake nose and a fake mustache
- yet somehow it works. The murder mystery contains quite a few
inconsistencies, plotholes and even cheats (which was not unusual for Mascot-serials:
There is no explanation as to Blaydon wants to on one hand build a tunnel
through Mystery Montain when he on the other hand wants to guard his
precious property, and why would the Rattler also make attacks on the
Corwin transportation company, oh, and how come Blayden, who is the
Rattler, has been seen alongside the Rattler in early episodes. Of course,
all this doesn't hurt the serial too much, as the emphasis is less on
logic and deduction but on all-out action - and on that account, Mystery
Mountain does just great.
By the way, cowboy star Ken Maynard was hired by Mascot to do
a feture - In Old Santa Fe - and two serials, Mystery Mountain
and Phantom Empire. And
even though both In Old Santa Fe and Mystery Mountain were
great successes for Mascot, Ken Maynard proved to difficult to work
with for Mascot president Nat Levine, so he let Maynard go
prematurely and gave the lead in Phantom
Empire to country singer and bit player Gene Autry, who had a bit
part in Mystery Mountain, shooting Ken out of his saddle at the end
of episode 6. The gamble proved successful, and Autry soon became one of
the greatest B-Western stars of his time.