At midnight on New Years Eve the S.S. Poseidon is struck by a 90′ tidal wave and is capsized. The Reverend Frank Scott leads nine Survivors; an elderly couple, Manny and Belle Rosen headed to Israel to see their grandson; A New York detective and his ex-prostitute wife, Mike and Linda Rogo on their second honeymoon to Italy; A young brother and sister, Robin and Susan Shelby going to meet their parents in Greece; A haberdasher James Martin; a pop singer Nonnie Parry, and a waiter from the ship Acres. They travel from the grand ballroom struggling through, steam, fire and rising water in the up-side-down ship to reach the bottom (the propeller shaft), now the top.

Scientist Jan Benes, who knows the secret to keeping soldiers shrunken for an indefinite period, escapes from behind the Iron Curtain with the help of CIA agent Grant. While being transferred, their motorcade is attacked. Benes strikes his head, causing a blood clot to form in his brain. Grant is ordered to accompany a group of scientists as they are miniaturized. The crew has one hour to get in Benes’s brain, remove the clot and get out.

Scott Calvin (Tim Allen) has been Santa Claus for the past eight years, and his loyal elves consider him the best Santa ever. But Santa’s got problems (he’s even mysteriously losing weight) and things quickly go south when he finds out that his son, Charlie, has landed on this year’s “naughty” list. Desperate to help his son, Scott heads back home, leaving a substitute Claus to watch over things at the Pole. But when the substitute institutes some strange redefinitions of naughty and nice, putting Christmas at risk, it’s up to Scott to return with a new bag of magic to try to save Christmas.