Deathworld

Jason dinAlt makes his living as a gambler with a talent for bending odds using unreliable psionic power, and has just won a fortune at the tables on Cassylia when Kerk Pyrrus, an ambassador from the deadliest world humans have ever colonized, challenges him to a different kind of game. Curious to meet someone who might be his equal, Jason follows Kerk home to Pyrrus, a planet of crushing gravity, savage weather, and every organism evolved to kill humans on contact, where his winnings are needed to buy weapons for a colony losing a war against its own environment. The first novel in Harry Harrison's Deathworld series.