Here's an guideline if you ever want to come up with your very own "original" Sci-Fi plot
1. Earth... (skip to 2, 9, or 14)
2. Burns up or freezes or falls into the sun... (skip to 3 or 4)
3. and everybody dies (The End)
4. and
almost everybody dies (The End)
5. is struck by a giant comet and... (6, 7, or 8)
6. is destroyed (The End)
7. is saved (The End)
8. is not destroyed but... (3 or 4)
9. scientists... (10 or 11)
10. discover... (12 or 13)
11. invent... (12 or 13)
12. tiny... (15, 16, 17, 18, or 19)
13. giant... (15, 16, 17, 18, or 19)
14. is attacked by Martian, Moon, Betelgeusian, or Extragalactic... (15, 16, 17, 18, or 19)
15. bug(s)... (20)
16. reptile(s)... (20)
17. mechanical device(s)... (20)
18. super persons... (20)
19. icky things... (20)
20. which/who... (21, 22, 23, 24, 25, or 26)
21. want our women... (27, 29, or 30)
22. are friendly (The End)
23. are friendly but misunderstood... (29 or 30)
24. misunderstand us... (29 or 30)
25. understand us too well... (29 or 30)
26. look upon us only as a source of nourishment... (28, 29, or 30)
27. and take a few and leave (The End)
28. and eat us (The End)
29. and are radioactive... (31 or 32)
30. and are not radioactive... (31 or 32)
31. and can be killed by... (33, 34, or 35)
32. and cannot be killed by... (36, 37, or 38)
33. the atomic bomb (The End)
34. the Army, Navy, Air Force, Marine Corps, and/or Coast Guard (The End)
35. a crowd of peasants with torches (The End)
36. the atomic bomb... (39, 40, 41, 42, 43, or 47)
37. the Army, Navy, Air Force, Marine Corps, and/or Coast Guard... (39, 40, 41, 42, 43, or 47)
38. a crowd of peasants with torches... (39, 40, 41, 42, 43, or 47)
39. but they die from catching chicken pox (The End)
40. so they kill us (The End)
41. so they put us under a benign dictatorship (The End)
42. so they eat us (The End)
43. so scientists invent a weapon... (44, 45, or 46)
44. which turns them into disgusting lumps (The End)
45. which kills them (The End)
46. which fails... (39, 40, 41, or 42)
47. but... (48, 49, or 50)
48. a cute little kid convinces them people are okay... (51, 52, or 53)
49. a priest talks to them of God... (51, 52, or 53)
50. they fall in love with this beautiful girl... (51, 52, 53, or 54)
51. and they die (The End)
52. and they leave (The End)
53. and they turn into disgusting lumps (The End)
54. and they get married and live happily forever after (The End)
... ;D