Oceans of Venus (original 1954; edition 1974)

VENUS: BEAUTIFUL AND DEADLY

   When Lucky Starr learned that Councilman Lou Evans, his roommate from the academy, had been charged with treason on Venus, Lucky took over the case. Someone was hypnotizing citizens, forcing them to act against their wills ... and afterward none could remember what they had done  - or why.
   Councilman Evans was accused of stealing classified information that  fragile economy. But Lucky just couldn't believe that Lou Evans was a criminal and a traitor to the Council.
   As he tried to solve the mystery, Lucky found himself pitted against the largest sea monster in the solar System. 
It had only one objective: Destroy Lucky Starr.
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CRASH LANDING

   "WE aren't leveling off," said Lucky grimly, working desperately to control the angle of flight. The blue surface of Venus was much closer, it was rushing at them.
   Lucky's fist closed more tightly on the duorod, squeezing the forks together. He dared not exert force too rapidly or the alleons might be whipped off by the screaming gale that flung itself past their ship. Yet there was only five hundred feet to spare before zero altitude.
   His nostrils flaring, the cords in his neck standing out, Lucky played those allerons against the wind.
    "We;re leveling," breathed Bigman. "We're leveling - "
   Bu the blue-green came up and up till it filled all the view in the port. Then, the Venus Marvel?, carrying Lucky Starr and Bigman Jones, struck the surface of the planet Venus ...